<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://corporate.comcast.com/role/AccountingPoliciesPolicies" xlink:href="cmcsa-20180331.xsd#AccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CommitmentsAndContingencies" xlink:href="cmcsa-20180331.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:href="cmcsa-20180331.xsd#CommitmentsAndContingenciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheet" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedBalanceSheet" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheetParenthetical" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedBalanceSheetParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedFinancialStatements" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedFinancialStatements" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfCashFlows" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedStatementOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfChangesInEquity" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedStatementOfChangesInEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncome" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedStatementOfComprehensiveIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfIncome" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatedStatementOfIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformation" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingBalanceSheetDetails" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformationCondensedConsolidatingBalanceSheetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfCashFlowsDetails" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfCashFlowsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfIncomeDetails" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationNarrativeDetails" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformationNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationTables" xlink:href="cmcsa-20180331.xsd#CondensedConsolidatingFinancialInformationTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/DocumentAndEntityInformation" xlink:href="cmcsa-20180331.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShare" xlink:href="cmcsa-20180331.xsd#EarningsPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShareDetails" xlink:href="cmcsa-20180331.xsd#EarningsPerShareDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShareTables" xlink:href="cmcsa-20180331.xsd#EarningsPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/FilmAndTelevisionCosts" xlink:href="cmcsa-20180331.xsd#FilmAndTelevisionCosts" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/FilmAndTelevisionCostsFilmAndTelevisionCostsdetails" xlink:href="cmcsa-20180331.xsd#FilmAndTelevisionCostsFilmAndTelevisionCostsdetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/FilmAndTelevisionCostsTables" xlink:href="cmcsa-20180331.xsd#FilmAndTelevisionCostsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/Investments" xlink:href="cmcsa-20180331.xsd#Investments" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsEquityMethodDetails" xlink:href="cmcsa-20180331.xsd#InvestmentsEquityMethodDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:href="cmcsa-20180331.xsd#InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsMarketableEquitySecuritiesDetails" xlink:href="cmcsa-20180331.xsd#InvestmentsMarketableEquitySecuritiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsOtherInvestmentsDetails" xlink:href="cmcsa-20180331.xsd#InvestmentsOtherInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsScheduleOfInvestmentsDetails" xlink:href="cmcsa-20180331.xsd#InvestmentsScheduleOfInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsTables" xlink:href="cmcsa-20180331.xsd#InvestmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebt" xlink:href="cmcsa-20180331.xsd#LongTermDebt" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtCommercialPaperProgramsDetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtCommercialPaperProgramsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtCrossGuaranteeStructureDetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtCrossGuaranteeStructureDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtDebtBorrowingsdetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtDebtBorrowingsdetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtDebtRepaymentsDetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtDebtRepaymentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtNarrativeDetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtRevolvingCreditFacilitiesDetails" xlink:href="cmcsa-20180331.xsd#LongTermDebtRevolvingCreditFacilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtTables" xlink:href="cmcsa-20180331.xsd#LongTermDebtTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReform" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReform" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionCableCommunicationsSegmentDetails" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionCableCommunicationsSegmentDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionStatementOfIncomeDetails" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionStatementOfIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectsOfChangesInRevenueRecognitionBalanceSheetDetails" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReformEffectsOfChangesInRevenueRecognitionBalanceSheetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformNarrativeDetails" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReformNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformTables" xlink:href="cmcsa-20180331.xsd#RecentAccountingPronouncementsAndTaxReformTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RelatedPartyTransactions" xlink:href="cmcsa-20180331.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RelatedPartyTransactionsCondensedConsolidatedBalanceSheetDetails" xlink:href="cmcsa-20180331.xsd#RelatedPartyTransactionsCondensedConsolidatedBalanceSheetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RelatedPartyTransactionsCondensedConsolidatedStatementOfIncomeDetails" xlink:href="cmcsa-20180331.xsd#RelatedPartyTransactionsCondensedConsolidatedStatementOfIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:href="cmcsa-20180331.xsd#RelatedPartyTransactionsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RelatedPartyTransactionsTables" xlink:href="cmcsa-20180331.xsd#RelatedPartyTransactionsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/Revenue" xlink:href="cmcsa-20180331.xsd#Revenue" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueCondensedConsolidatedBalanceSheetDetails" xlink:href="cmcsa-20180331.xsd#RevenueCondensedConsolidatedBalanceSheetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueDetails" xlink:href="cmcsa-20180331.xsd#RevenueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueNarrativeDetails" xlink:href="cmcsa-20180331.xsd#RevenueNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueRevenueByGeographicLocationDetails" xlink:href="cmcsa-20180331.xsd#RevenueRevenueByGeographicLocationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueTables" xlink:href="cmcsa-20180331.xsd#RevenueTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformation" xlink:href="cmcsa-20180331.xsd#SegmentInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationDetails" xlink:href="cmcsa-20180331.xsd#SegmentInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:href="cmcsa-20180331.xsd#SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationTables" xlink:href="cmcsa-20180331.xsd#SegmentInformationTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SignificantTransactions" xlink:href="cmcsa-20180331.xsd#SignificantTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SignificantTransactionsSkyOfferDetails" xlink:href="cmcsa-20180331.xsd#SignificantTransactionsSkyOfferDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SignificantTransactionsUniversalBeijingResortDetails" xlink:href="cmcsa-20180331.xsd#SignificantTransactionsUniversalBeijingResortDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformation" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesdetails" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesdetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationNoncashInvestingAndFinancingActivitiesdetails" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationNoncashInvestingAndFinancingActivitiesdetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationShareBasedCompensationDetails" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationShareBasedCompensationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationTables" xlink:href="cmcsa-20180331.xsd#SupplementalFinancialInformationTables" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/AccountingPoliciesPolicies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_8619CB48B61998315722F822B5903E76" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_8619CB48B61998315722F822B5903E76" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_F80DF985E33B9D9F73FFF822B590F84E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_8619CB48B61998315722F822B5903E76" xlink:to="loc_dei_LegalEntityAxis_F80DF985E33B9D9F73FFF822B590F84E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F1A0981E836772FFB8FCF822B5915341_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_F80DF985E33B9D9F73FFF822B590F84E" xlink:to="loc_dei_EntityDomain_F1A0981E836772FFB8FCF822B5915341_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F1A0981E836772FFB8FCF822B5915341" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_F80DF985E33B9D9F73FFF822B590F84E" xlink:to="loc_dei_EntityDomain_F1A0981E836772FFB8FCF822B5915341" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_878EF4E1C779F9F434BBF822B5917DDE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_F1A0981E836772FFB8FCF822B5915341" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_878EF4E1C779F9F434BBF822B5917DDE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_CA414D15D8EA0682D3C9F822B5915744" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_CA414D15D8EA0682D3C9F822B5915744" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:label="loc_us-gaap_RevenueRecognitionPolicyTextBlock_2903B599ACF9CD0B4BD1F822B5917282" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:to="loc_us-gaap_RevenueRecognitionPolicyTextBlock_2903B599ACF9CD0B4BD1F822B5917282" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_98A44636FEFFB90544D0F822B5915A31" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:to="loc_us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_98A44636FEFFB90544D0F822B5915A31" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentPolicyTextBlock" xlink:label="loc_us-gaap_InvestmentPolicyTextBlock_D1E1D5A4673C507EE67EF822B5928EB6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_6B44C5358831336A8DEFF822B591C8B1" xlink:to="loc_us-gaap_InvestmentPolicyTextBlock_D1E1D5A4673C507EE67EF822B5928EB6" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TemporaryEquityLineItems" xlink:label="loc_us-gaap_TemporaryEquityLineItems_DD4CB3FF514240827089FC1E3661DEAC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TemporaryEquityByClassOfStockTable" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_AB62E135253F2D1C4880FC1E36617160" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_DD4CB3FF514240827089FC1E3661DEAC" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_AB62E135253F2D1C4880FC1E36617160" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_3F5C1915405792EA2F7DFC1E3661BACD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_AB62E135253F2D1C4880FC1E36617160" xlink:to="loc_us-gaap_StatementClassOfStockAxis_3F5C1915405792EA2F7DFC1E3661BACD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_949E6F65DE51D25A5B55FC1E3661DCE4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3F5C1915405792EA2F7DFC1E3661BACD" xlink:to="loc_us-gaap_ClassOfStockDomain_949E6F65DE51D25A5B55FC1E3661DCE4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_949E6F65DE51D25A5B55FC1E3661DCE4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3F5C1915405792EA2F7DFC1E3661BACD" xlink:to="loc_us-gaap_ClassOfStockDomain_949E6F65DE51D25A5B55FC1E3661DCE4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemablePreferredStockMember" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_1BCC1D2D8CBDB5B09A98FC1E366105E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_949E6F65DE51D25A5B55FC1E3661DCE4" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_1BCC1D2D8CBDB5B09A98FC1E366105E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44C5D77B2A0AC015F367FC1E3661ACC8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_AB62E135253F2D1C4880FC1E36617160" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44C5D77B2A0AC015F367FC1E3661ACC8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_700509BAB68507A4184AFC1E36613C5F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44C5D77B2A0AC015F367FC1E3661ACC8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_700509BAB68507A4184AFC1E36613C5F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_700509BAB68507A4184AFC1E36613C5F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44C5D77B2A0AC015F367FC1E3661ACC8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_700509BAB68507A4184AFC1E36613C5F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_3714DB288FADFAC26C3BFC1E3661FE5E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_700509BAB68507A4184AFC1E36613C5F" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_3714DB288FADFAC26C3BFC1E3661FE5E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock_5FCB69280DCA6285FEE9FC1E36611CDF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_DD4CB3FF514240827089FC1E3661DEAC" xlink:to="loc_cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock_5FCB69280DCA6285FEE9FC1E36611CDF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheet" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_5ED49674330A1E858AC7BAB16CC9B007" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A53D9F6F63A299B69C0EBAB16CC8926F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5ED49674330A1E858AC7BAB16CC9B007" xlink:to="loc_us-gaap_StatementTable_A53D9F6F63A299B69C0EBAB16CC8926F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_CB4B956FC51B8E657803BAB16CC8E4F3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A53D9F6F63A299B69C0EBAB16CC8926F" xlink:to="loc_us-gaap_StatementClassOfStockAxis_CB4B956FC51B8E657803BAB16CC8E4F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_CB4B956FC51B8E657803BAB16CC8E4F3" xlink:to="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_CB4B956FC51B8E657803BAB16CC8E4F3" xlink:to="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_25A65FB25F1BF5A30309BAB16CC9C264" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D" xlink:to="loc_us-gaap_CommonClassAMember_25A65FB25F1BF5A30309BAB16CC9C264" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_07E08E7E186D1D7A12C1BAB16CC99044" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6CC03058BDE38A96C9B3BAB16CC8976D" xlink:to="loc_us-gaap_CommonClassBMember_07E08E7E186D1D7A12C1BAB16CC99044" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_B124B31ED02E355F5E79BAB16CC9C77A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A53D9F6F63A299B69C0EBAB16CC8926F" xlink:to="loc_dei_LegalEntityAxis_B124B31ED02E355F5E79BAB16CC9C77A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F5789D29291602D2C75BBAB16CC9041F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_B124B31ED02E355F5E79BAB16CC9C77A" xlink:to="loc_dei_EntityDomain_F5789D29291602D2C75BBAB16CC9041F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F5789D29291602D2C75BBAB16CC9041F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_B124B31ED02E355F5E79BAB16CC9C77A" xlink:to="loc_dei_EntityDomain_F5789D29291602D2C75BBAB16CC9041F" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_7A85EB972DA2B0E1809BBAB16CC9E6FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_F5789D29291602D2C75BBAB16CC9041F" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_7A85EB972DA2B0E1809BBAB16CC9E6FB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5ED49674330A1E858AC7BAB16CC9B007" xlink:to="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_5BBC2A0FF6DCB7337B4BBAB16CC9E756" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_5BBC2A0FF6DCB7337B4BBAB16CC9E756" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_2AF20F849EA6D14E0907BAB16CC9DCAB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_2AF20F849EA6D14E0907BAB16CC9DCAB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingRightsCurrent" xlink:label="loc_cmcsa_ProgrammingRightsCurrent_B0A3C54B620E1BF20A98BAB16CC936B5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:to="loc_cmcsa_ProgrammingRightsCurrent_B0A3C54B620E1BF20A98BAB16CC936B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="loc_us-gaap_OtherAssetsCurrent_7CA774F5F0F152ECB419BAB16CC96DDE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:to="loc_us-gaap_OtherAssetsCurrent_7CA774F5F0F152ECB419BAB16CC96DDE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_B4616D38E817F75BBBCEBAB16CC96189" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_232C3DBA5ADACD1959B6BAB16CC9C84B" xlink:to="loc_us-gaap_AssetsCurrent_B4616D38E817F75BBBCEBAB16CC96189" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCosts" xlink:label="loc_cmcsa_FilmAndTelevisionCosts_5D93FEA3227A54400836BAB16CC9109F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_cmcsa_FilmAndTelevisionCosts_5D93FEA3227A54400836BAB16CC9109F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermInvestments" xlink:label="loc_us-gaap_LongTermInvestments_7C9C04F874A128EB1E72BAB16CC98926" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_LongTermInvestments_7C9C04F874A128EB1E72BAB16CC98926" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_49F306CD69EFB1043404BAB16CC97CA7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_49F306CD69EFB1043404BAB16CC97CA7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedFranchiseRights" xlink:label="loc_us-gaap_IndefiniteLivedFranchiseRights_ADD1B7535DD0B1B0D5E8BAB16CCAD2D1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_IndefiniteLivedFranchiseRights_ADD1B7535DD0B1B0D5E8BAB16CCAD2D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_039F30BACFE80C918124BAB16CCA1863" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_Goodwill_039F30BACFE80C918124BAB16CCA1863" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="loc_us-gaap_OtherIntangibleAssetsNet_85667DD30DC0B82223DDBAB16CCA093B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_OtherIntangibleAssetsNet_85667DD30DC0B82223DDBAB16CCA093B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_896542B893142079A51EBAB16CCAD0DA" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_896542B893142079A51EBAB16CCAD0DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_62BC30053442A250932FBAB16CCA99D7" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_62BC30053442A250932FBAB16CCA99D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_F0891A550CBDE6C9EFA5BAB16CCA5FC7" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_D8C3342790F80C70D747BAB16CC9176A" xlink:to="loc_us-gaap_Assets_F0891A550CBDE6C9EFA5BAB16CCA5FC7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5ED49674330A1E858AC7BAB16CC9B007" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_9551273E5C36DF946FE7BAB16CCAA1A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_AccountsPayableCurrent_9551273E5C36DF946FE7BAB16CCAA1A9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AccruedParticipationsAndResidualsCurrent" xlink:label="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_408DACB1E89D98EFFE15BAB16CCA07E0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_408DACB1E89D98EFFE15BAB16CCA07E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProgramRightsObligationsCurrent" xlink:label="loc_us-gaap_ProgramRightsObligationsCurrent_C6EE7F6264FC704E3843BAB16CCAE8E3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_ProgramRightsObligationsCurrent_C6EE7F6264FC704E3843BAB16CCAE8E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_726DA1F956F869EE0CCBBAB16CCA2E56" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_DeferredRevenueCurrent_726DA1F956F869EE0CCBBAB16CCA2E56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_FA1643B54959A201ADF3BAB16CCA3C26" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_FA1643B54959A201ADF3BAB16CCA3C26" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NotePayableToUltimateParent" xlink:label="loc_cmcsa_NotePayableToUltimateParent_B01AA6FD9757F23802B8BAB16CCA3423" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_cmcsa_NotePayableToUltimateParent_B01AA6FD9757F23802B8BAB16CCA3423" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtCurrent" xlink:label="loc_us-gaap_DebtCurrent_D7AFD8EECDF6F4431A39BAB16CCA664B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_DebtCurrent_D7AFD8EECDF6F4431A39BAB16CCA664B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_7763FDB110D8CD69BBBFBAB16CCADC76" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_EC362E9BB97A014075E6BAB16CCA0C1D" xlink:to="loc_us-gaap_LiabilitiesCurrent_7763FDB110D8CD69BBBFBAB16CCADC76" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_B13B53047FEF87935765BAB16CCA5306" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_B13B53047FEF87935765BAB16CCA5306" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AccruedParticipationsResidualsAndProgramObligationsNoncurrent" xlink:label="loc_cmcsa_AccruedParticipationsResidualsAndProgramObligationsNoncurrent_6B34788027CE1C61E6DCBAB16CCA8DC9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_cmcsa_AccruedParticipationsResidualsAndProgramObligationsNoncurrent_6B34788027CE1C61E6DCBAB16CCA8DC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_43CFE3EB05F561300C14BAB16CCB574E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_43CFE3EB05F561300C14BAB16CCB574E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_EBE00DC1A13438C5F161BAB16CCBCD38" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_EBE00DC1A13438C5F161BAB16CCBCD38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_D6F3E8BA92A02BCF7CE1BAB16CCBA491" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_CommitmentsAndContingencies_D6F3E8BA92A02BCF7CE1BAB16CCBA491" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_E28A008DF6DC0207AFD4BAB16CCB7A04" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_E28A008DF6DC0207AFD4BAB16CCB7A04" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_3B85FFF3E26E4942B4BABAB16CCBB99D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_PreferredStockValue_3B85FFF3E26E4942B4BABAB16CCBB99D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_9DC39164C58DA794DE67BAB16CCB88F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_CommonStockValue_9DC39164C58DA794DE67BAB16CCB88F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_7FAF1244D6FE8AA1646ABAB16CCBB9A4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_AdditionalPaidInCapital_7FAF1244D6FE8AA1646ABAB16CCBB9A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_0ACB1A064575B408CB2ABAB16CCB8B1C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_0ACB1A064575B408CB2ABAB16CCB8B1C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="loc_us-gaap_TreasuryStockValue_104ED80F1FA7B23160D6BAB16CCB3CB4" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_TreasuryStockValue_104ED80F1FA7B23160D6BAB16CCB3CB4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersCapital" xlink:label="loc_us-gaap_MembersCapital_C72D64769E6B738032EDBAB16CCB3BAB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_MembersCapital_C72D64769E6B738032EDBAB16CCB3BAB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_66B9A44A1DCE6AAD6D54BAB16CCB1191" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_66B9A44A1DCE6AAD6D54BAB16CCB1191" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersEquity" xlink:label="loc_us-gaap_MembersEquity_950AE0049BB063C933A8BAB16CCBAD1B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_MembersEquity_950AE0049BB063C933A8BAB16CCBAD1B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_27FDE107C40FAD2970C9BAB16CCB8395" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_StockholdersEquity_27FDE107C40FAD2970C9BAB16CCB8395" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersEquityAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_MembersEquityAttributableToNoncontrollingInterest_E7F9F1557C8623C2C80DBAB16CCB6E3F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_MembersEquityAttributableToNoncontrollingInterest_E7F9F1557C8623C2C80DBAB16CCB6E3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_AB4F6969EDFF89619E72BAB16CCB5145" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_MinorityInterest_AB4F6969EDFF89619E72BAB16CCB5145" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_93A846F44AA5AAB4C466BAB16CCB9274" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_93A846F44AA5AAB4C466BAB16CCB9274" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_A425DC21AEA1F138C639BAB16CCBAA53" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_5C64D0DAD578294EC929BAB16CCBB7A7" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_A425DC21AEA1F138C639BAB16CCBAA53" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_5AD2350CA5E8F40BFDF1BAB16CCC4013" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_B3141995FE6660CDEE57BAB16CCAD362" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_5AD2350CA5E8F40BFDF1BAB16CCC4013" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheetParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_B173F0C4C2D7B58F8230D9C80A40BB98" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_StatementTable_B173F0C4C2D7B58F8230D9C80A40BB98" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ABD07A43A50990A5F3B6D9C80A40D6B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_B173F0C4C2D7B58F8230D9C80A40BB98" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ABD07A43A50990A5F3B6D9C80A40D6B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ABD07A43A50990A5F3B6D9C80A40D6B7" xlink:to="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ABD07A43A50990A5F3B6D9C80A40D6B7" xlink:to="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_CE692B0089924665B5F6D9C80A40CDD0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44" xlink:to="loc_us-gaap_CommonClassAMember_CE692B0089924665B5F6D9C80A40CDD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_58CC00D90B739CFF4296D9C80A41D814" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_31C9F228813F286F636CD9C80A405E44" xlink:to="loc_us-gaap_CommonClassBMember_58CC00D90B739CFF4296D9C80A41D814" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1B12156232B03607A2F7D9C80A4112EC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_B173F0C4C2D7B58F8230D9C80A40BB98" xlink:to="loc_dei_LegalEntityAxis_1B12156232B03607A2F7D9C80A4112EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_02960517842405A47C57D9C80A419916_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1B12156232B03607A2F7D9C80A4112EC" xlink:to="loc_dei_EntityDomain_02960517842405A47C57D9C80A419916_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_02960517842405A47C57D9C80A419916" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1B12156232B03607A2F7D9C80A4112EC" xlink:to="loc_dei_EntityDomain_02960517842405A47C57D9C80A419916" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_C82BE970BF3F420C7EA3D9C80A416B54" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_02960517842405A47C57D9C80A419916" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_C82BE970BF3F420C7EA3D9C80A416B54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_37970BBE7E8202308E0AD9C80A46386C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_37970BBE7E8202308E0AD9C80A46386C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_7A22E5E714B9D6D6AC15D9C80A4634BF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_7A22E5E714B9D6D6AC15D9C80A4634BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_08F010AA4452D255C524D9C80A47794D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_08F010AA4452D255C524D9C80A47794D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="loc_us-gaap_PreferredStockSharesIssued_C5070D4B1920910363CCD9C80A4768AA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_PreferredStockSharesIssued_C5070D4B1920910363CCD9C80A4768AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_0AC81145C9A3C935CA0BD9C80A4799DA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_0AC81145C9A3C935CA0BD9C80A4799DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_E150A3D203995D9A775DD9C80A4749EF" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_E150A3D203995D9A775DD9C80A4749EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_10B93D9FCBEB29FCC4B7D9C80A476D8D" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_CommonStockSharesIssued_10B93D9FCBEB29FCC4B7D9C80A476D8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_E403455EB095033DC489D9C80A475DAE" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_E403455EB095033DC489D9C80A475DAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="loc_us-gaap_TreasuryStockShares_926E0F20AC66ABE3A4FED9C80A47B3BD" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_64FE669C9391BE6E6671D9C80A46456E" xlink:to="loc_us-gaap_TreasuryStockShares_926E0F20AC66ABE3A4FED9C80A47B3BD" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedFinancialStatements" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAndBasisOfPresentationLineItems" xlink:label="loc_cmcsa_BusinessAndBasisOfPresentationLineItems_077D455FE7E6E27941E8FC1E376E4FE3" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAndBasisOfPresentationTable" xlink:label="loc_cmcsa_BusinessAndBasisOfPresentationTable_A0984B9AE07546D0B0B7FC1E376E65B4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_BusinessAndBasisOfPresentationLineItems_077D455FE7E6E27941E8FC1E376E4FE3" xlink:to="loc_cmcsa_BusinessAndBasisOfPresentationTable_A0984B9AE07546D0B0B7FC1E376E65B4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_CF948A8E3BAEE010D6BBFC1E376E45F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_BusinessAndBasisOfPresentationTable_A0984B9AE07546D0B0B7FC1E376E65B4" xlink:to="loc_dei_LegalEntityAxis_CF948A8E3BAEE010D6BBFC1E376E45F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0C026B680CD7EA642FB4FC1E376E978B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_CF948A8E3BAEE010D6BBFC1E376E45F4" xlink:to="loc_dei_EntityDomain_0C026B680CD7EA642FB4FC1E376E978B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0C026B680CD7EA642FB4FC1E376E978B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_CF948A8E3BAEE010D6BBFC1E376E45F4" xlink:to="loc_dei_EntityDomain_0C026B680CD7EA642FB4FC1E376E978B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_357DB4928309570496F4FC1E376EB58E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0C026B680CD7EA642FB4FC1E376E978B" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_357DB4928309570496F4FC1E376EB58E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessDescriptionAndBasisOfPresentationTextBlock" xlink:label="loc_us-gaap_BusinessDescriptionAndBasisOfPresentationTextBlock_01B68096253D8BBB82EAFC1E376E84FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_BusinessAndBasisOfPresentationLineItems_077D455FE7E6E27941E8FC1E376E4FE3" xlink:to="loc_us-gaap_BusinessDescriptionAndBasisOfPresentationTextBlock_01B68096253D8BBB82EAFC1E376E84FC" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfCashFlows" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_490CEDFB9D1A41F554EFF3D8482485E7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_StatementTable_490CEDFB9D1A41F554EFF3D8482485E7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_55D68A8A84BA542DA931F3D84824B2CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_490CEDFB9D1A41F554EFF3D8482485E7" xlink:to="loc_dei_LegalEntityAxis_55D68A8A84BA542DA931F3D84824B2CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D92A522161BA0E8F636DF3D848242AD0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_55D68A8A84BA542DA931F3D84824B2CB" xlink:to="loc_dei_EntityDomain_D92A522161BA0E8F636DF3D848242AD0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D92A522161BA0E8F636DF3D848242AD0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_55D68A8A84BA542DA931F3D84824B2CB" xlink:to="loc_dei_EntityDomain_D92A522161BA0E8F636DF3D848242AD0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_A909E5CCFD63ABF44A6CF3D8482423C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D92A522161BA0E8F636DF3D848242AD0" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_A909E5CCFD63ABF44A6CF3D8482423C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_FF6D6DC45208DB0EF0D8F3D848247ABD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:to="loc_us-gaap_ProfitLoss_FF6D6DC45208DB0EF0D8F3D848247ABD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="loc_us-gaap_DepreciationAndAmortization_2F450F249BEEFFE66691F3D84824D65B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:to="loc_us-gaap_DepreciationAndAmortization_2F450F249BEEFFE66691F3D84824D65B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_5743A0492F4B9EF9C083F3D84824E33D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:to="loc_us-gaap_ShareBasedCompensation_5743A0492F4B9EF9C083F3D84824E33D" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NoncashInterestExpenseIncomeNet" xlink:label="loc_cmcsa_NoncashInterestExpenseIncomeNet_11F42BA749C5697886FFF3D8482489A0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:to="loc_cmcsa_NoncashInterestExpenseIncomeNet_11F42BA749C5697886FFF3D8482489A0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GainLossOnInvestmentsAndOtherNoncashIncomeLossNet" xlink:label="loc_cmcsa_GainLossOnInvestmentsAndOtherNoncashIncomeLossNet_5BEBCFC9DC4014D8C732F3D84824C0A2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:to="loc_cmcsa_GainLossOnInvestmentsAndOtherNoncashIncomeLossNet_5BEBCFC9DC4014D8C732F3D84824C0A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_987BBFF5F1C39A475BF1F3D848243B69" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_48341F87EC21FAF54D25F3D848240742" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_987BBFF5F1C39A475BF1F3D848243B69" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ChangeInCurrentAndNoncurrentReceivablesNet" xlink:label="loc_cmcsa_ChangeInCurrentAndNoncurrentReceivablesNet_C99BA92BCF77F1B15CD3F3D84824E632" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:to="loc_cmcsa_ChangeInCurrentAndNoncurrentReceivablesNet_C99BA92BCF77F1B15CD3F3D84824E632" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Increasedecreaseinfilmandtelevisioncostnet" xlink:label="loc_cmcsa_Increasedecreaseinfilmandtelevisioncostnet_BF19C9BEC082778CD6F1F3D848245B71" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:to="loc_cmcsa_Increasedecreaseinfilmandtelevisioncostnet_BF19C9BEC082778CD6F1F3D848245B71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_E4F0427E5D1C1F9C06E7F3D848244B19" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_E4F0427E5D1C1F9C06E7F3D848244B19" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_561152D5B44BBADC52F0F3D84824B337" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_D8CF56EB22B1050DFCDEF3D84824F3D7" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_561152D5B44BBADC52F0F3D84824B337" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_1574D403AA06E1C9334FF3D84824FDDC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_C45EBB69719CDD192FC8F3D84824D48D" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_1574D403AA06E1C9334FF3D84824FDDC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_3037B9EE354A23FEF180F3D848246370" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_3037B9EE354A23FEF180F3D848246370" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_6A86A5F42E88C61CF8B8F3D84824903B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_6A86A5F42E88C61CF8B8F3D84824903B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties" xlink:label="loc_cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties_0D3584B631036797DF28F3D848246A88" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties_0D3584B631036797DF28F3D848246A88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8CA87EC8038409641D36F3D848240F35" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8CA87EC8038409641D36F3D848240F35" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProceedsFromSalesOfBusinessesAndInvestments" xlink:label="loc_cmcsa_ProceedsFromSalesOfBusinessesAndInvestments_80F5BD92CD299E8DA03CF3D848240EE5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_cmcsa_ProceedsFromSalesOfBusinessesAndInvestments_80F5BD92CD299E8DA03CF3D848240EE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_141A51524ECE50E29CD8F3D84824DA97" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_141A51524ECE50E29CD8F3D84824DA97" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_471171C3FD385F8E9D9EF3D84824BC1E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_471171C3FD385F8E9D9EF3D84824BC1E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_FD76D619E068EC3CD27BF3D84824B575" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4026FF91D93A2E460A7BF3D84824E6F4" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_FD76D619E068EC3CD27BF3D84824B575" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromRepaymentsOfShortTermDebt" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_E18D5366C50435F25E12F3D848245F72" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_E18D5366C50435F25E12F3D848245F72" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_BB53E57F1F87094D3E82F3D848247EDA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_BB53E57F1F87094D3E82F3D848247EDA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfOtherDebt" xlink:label="loc_us-gaap_RepaymentsOfOtherDebt_9F58D77DF6DB0482EA4CF3D848247B12" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_RepaymentsOfOtherDebt_9F58D77DF6DB0482EA4CF3D848247B12" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProceedsFromNoteReceivableIssuedToAndBorrowingsFromUltimateParent" xlink:label="loc_cmcsa_ProceedsFromNoteReceivableIssuedToAndBorrowingsFromUltimateParent_E6D691D2ACE90135C253F3D84824BB81" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_cmcsa_ProceedsFromNoteReceivableIssuedToAndBorrowingsFromUltimateParent_E6D691D2ACE90135C253F3D84824BB81" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_BA2E18266C44DCDC8F1AF3D84824FA16" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_BA2E18266C44DCDC8F1AF3D84824FA16" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDividends" xlink:label="loc_us-gaap_PaymentsOfDividends_4A6DFB9FE04E345120F3F3D848243700" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_PaymentsOfDividends_4A6DFB9FE04E345120F3F3D848243700" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock_17B1900FCF282B972487F3D84824DD92" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock_17B1900FCF282B972487F3D84824DD92" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfCapitalDistribution" xlink:label="loc_us-gaap_PaymentsOfCapitalDistribution_491673FFDEF3C2CA63A5F3D84824AAF0" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_PaymentsOfCapitalDistribution_491673FFDEF3C2CA63A5F3D84824AAF0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Distributionstononcontrollinginterestholders" xlink:label="loc_cmcsa_Distributionstononcontrollinginterestholders_0FBA6BEB057EE513D230F3D84824C137" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_cmcsa_Distributionstononcontrollinginterestholders_0FBA6BEB057EE513D230F3D84824C137" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_AD021423AE6B4D831CC3F3D84824BE3A" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_AD021423AE6B4D831CC3F3D84824BE3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_D656A87C8CB18302E2DAF3D84824BDC2" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_D86E46F7C5A980AC0D06F3D848247B43" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_D656A87C8CB18302E2DAF3D84824BDC2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_BF5EE089C6A942E043EBF3D84824DA9B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_BF5EE089C6A942E043EBF3D84824DA9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_DB09B80132D1286778BDF3D84824532A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_1C15A1AF289827103288F3D8482489B9" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_DB09B80132D1286778BDF3D84824532A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfChangesInEquity" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_696CB023458A6ABBAF72E38047A26470" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_85455E964FAC6FCEAA57E38047955A99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_696CB023458A6ABBAF72E38047A26470" xlink:to="loc_us-gaap_StatementTable_85455E964FAC6FCEAA57E38047955A99" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_B9E438C0CE77BFD34275E380479E78E2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_85455E964FAC6FCEAA57E38047955A99" xlink:to="loc_us-gaap_StatementClassOfStockAxis_B9E438C0CE77BFD34275E380479E78E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_B9E438C0CE77BFD34275E380479E78E2" xlink:to="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_B9E438C0CE77BFD34275E380479E78E2" xlink:to="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_EC4208D09546B998232AE380479F2DFD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A" xlink:to="loc_us-gaap_CommonClassAMember_EC4208D09546B998232AE380479F2DFD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_A369B5B777FFAB564698E380479F9CFD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0B42745517538CA989B2E380479F575A" xlink:to="loc_us-gaap_CommonClassBMember_A369B5B777FFAB564698E380479F9CFD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_49A572533AB1BC9FF45CE380479FE338" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_85455E964FAC6FCEAA57E38047955A99" xlink:to="loc_dei_LegalEntityAxis_49A572533AB1BC9FF45CE380479FE338" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6FC1E332F6176D02155CE380479F5077_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_49A572533AB1BC9FF45CE380479FE338" xlink:to="loc_dei_EntityDomain_6FC1E332F6176D02155CE380479F5077_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6FC1E332F6176D02155CE380479F5077" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_49A572533AB1BC9FF45CE380479FE338" xlink:to="loc_dei_EntityDomain_6FC1E332F6176D02155CE380479F5077" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_803E35FB1CD4B5408A6DE380479FF925" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6FC1E332F6176D02155CE380479F5077" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_803E35FB1CD4B5408A6DE380479FF925" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_4D92391ADD08EE15DE6BE38047A00E98" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_85455E964FAC6FCEAA57E38047955A99" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_4D92391ADD08EE15DE6BE38047A00E98" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4D92391ADD08EE15DE6BE38047A00E98" xlink:to="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4D92391ADD08EE15DE6BE38047A00E98" xlink:to="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember" xlink:label="loc_cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember_FD6BD6B200C409B2B646E38047A1C872" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember_FD6BD6B200C409B2B646E38047A1C872" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RedeemableNoncontrollingInterestMember" xlink:label="loc_cmcsa_RedeemableNoncontrollingInterestMember_1101E5FB06966EC98377E38047A148A1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_cmcsa_RedeemableNoncontrollingInterestMember_1101E5FB06966EC98377E38047A148A1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_MembersCapitalMember" xlink:label="loc_cmcsa_MembersCapitalMember_C95155663F2CABDCBB4CE38047A1F090" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_cmcsa_MembersCapitalMember_C95155663F2CABDCBB4CE38047A1F090" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_CBC384A95B71C2E35AB6E38047A17704" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_CommonStockMember_CBC384A95B71C2E35AB6E38047A17704" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_90888322C213C542E80AE38047A15B13" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_90888322C213C542E80AE38047A15B13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_FA1A114790F37F449880E38047A2ADE8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_RetainedEarningsMember_FA1A114790F37F449880E38047A2ADE8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="loc_us-gaap_TreasuryStockMember_EBE986937709ADDE79D7E38047A29A5C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_TreasuryStockMember_EBE986937709ADDE79D7E38047A29A5C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F73D1507781A8E9FA0CBE38047A204F0" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F73D1507781A8E9FA0CBE38047A204F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_EB628D386CD79047E36DE38047A27975" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_F45AEFCE7563E9D8418CE38047A0C21C" xlink:to="loc_us-gaap_NoncontrollingInterestMember_EB628D386CD79047E36DE38047A27975" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_696CB023458A6ABBAF72E38047A26470" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_91353FD3E1FD0B7B4035E38047A3224E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_91353FD3E1FD0B7B4035E38047A3224E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_97F36F27077F6408FC7BE38047A3B9CD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_97F36F27077F6408FC7BE38047A3B9CD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_283F72AD4EB9B6DE0912E38047A47A85" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_283F72AD4EB9B6DE0912E38047A47A85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_8B132D7E146F96EA8FE8E38047A41986" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_8B132D7E146F96EA8FE8E38047A41986" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_DE43FCB784EF24F3EE93E38047A4D281" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_DE43FCB784EF24F3EE93E38047A4D281" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_E16C467E8BACBE6B8DDCE38047A418AB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_E16C467E8BACBE6B8DDCE38047A418AB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="loc_us-gaap_DividendsCommonStockCash_598A857E6497723211BBE38047A4C8EC" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_DividendsCommonStockCash_598A857E6497723211BBE38047A4C8EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1002A978659168BB4D8CE38047A46774" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1002A978659168BB4D8CE38047A46774" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests" xlink:label="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests_BFED5758F5D885D43705E38047A5B52B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests_BFED5758F5D885D43705E38047A5B52B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_MemberContribution" xlink:label="loc_cmcsa_MemberContribution_DD254006911768946A6BE38047A59671" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_cmcsa_MemberContribution_DD254006911768946A6BE38047A59671" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityOther" xlink:label="loc_us-gaap_StockholdersEquityOther_286B5CDF047C6A6D2EBEE38047A5FACA" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_us-gaap_StockholdersEquityOther_286B5CDF047C6A6D2EBEE38047A5FACA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquityProfitLoss" xlink:label="loc_cmcsa_EquityProfitLoss_1A8A9C64AB3BA17B81A6E38047A51B7D" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1DAF03838EADBFDB1562E38047A33584" xlink:to="loc_cmcsa_EquityProfitLoss_1A8A9C64AB3BA17B81A6E38047A51B7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_696CB023458A6ABBAF72E38047A26470" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_D0B25E468FDE54F27784E38047A60FC3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_D0B25E468FDE54F27784E38047A60FC3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity" xlink:label="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity_B828AC05934427725EDBE38047A6E55E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:to="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity_B828AC05934427725EDBE38047A6E55E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TemporaryEquityOtherChanges" xlink:label="loc_us-gaap_TemporaryEquityOtherChanges_04070D858D70C0ABE375E38047A68B64" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:to="loc_us-gaap_TemporaryEquityOtherChanges_04070D858D70C0ABE375E38047A68B64" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_0114EEDFFC4440F3AAB3E38047A7FA83" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_D3323FE6CC62EE381789E38047A6A8DF" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_0114EEDFFC4440F3AAB3E38047A7FA83" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_1A7FF9D65EB855C0BF95BAB16CDF57DB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_StatementTable_1A7FF9D65EB855C0BF95BAB16CDF57DB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_EF30AF914C48E899A087BAB16CDF5FE7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1A7FF9D65EB855C0BF95BAB16CDF57DB" xlink:to="loc_dei_LegalEntityAxis_EF30AF914C48E899A087BAB16CDF5FE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_587D6BAC658CDD4500F3BAB16CDF2427_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_EF30AF914C48E899A087BAB16CDF5FE7" xlink:to="loc_dei_EntityDomain_587D6BAC658CDD4500F3BAB16CDF2427_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_587D6BAC658CDD4500F3BAB16CDF2427" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_EF30AF914C48E899A087BAB16CDF5FE7" xlink:to="loc_dei_EntityDomain_587D6BAC658CDD4500F3BAB16CDF2427" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_5B9B205E3D648D7C864CBAB16CE01F13" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_587D6BAC658CDD4500F3BAB16CDF2427" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_5B9B205E3D648D7C864CBAB16CE01F13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_6B0DEF8A722C738A6185BAB16CE042D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_ProfitLoss_6B0DEF8A722C738A6185BAB16CE042D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_4E710F491DE881CBD0EFBAB16CE0E266" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_4E710F491DE881CBD0EFBAB16CE0E266" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax_73E307F92655808FBB7EBAB16CE0A1F5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax_73E307F92655808FBB7EBAB16CE0A1F5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AmountsReclassifiedToNetIncomeAbstract" xlink:label="loc_cmcsa_AmountsReclassifiedToNetIncomeAbstract_55D6D81BB50B7A370B90BAB16CE00670" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_cmcsa_AmountsReclassifiedToNetIncomeAbstract_55D6D81BB50B7A370B90BAB16CE00670" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax_742BE3430BC8F7571389BAB16CE05E6C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_AmountsReclassifiedToNetIncomeAbstract_55D6D81BB50B7A370B90BAB16CE00670" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesNetOfTax_742BE3430BC8F7571389BAB16CE05E6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_B26AD4DD1FB5904EC8DDBAB16CE00DA2" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_B26AD4DD1FB5904EC8DDBAB16CE00DA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_67BD186616C06076BCA2BAB16CE0396F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_67BD186616C06076BCA2BAB16CE0396F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_057D3D8E46AF763138ABBAB16CE0ACB1" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_057D3D8E46AF763138ABBAB16CE0ACB1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_85F36555151D4106271EBAB16CE051CC" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_85F36555151D4106271EBAB16CE051CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_D750A46FF567377E9BAEBAB16CE0BB79" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_D750A46FF567377E9BAEBAB16CE0BB79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_FF39C97DB744DDF4EE47BAB16CE0CB22" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_FF39C97DB744DDF4EE47BAB16CE0CB22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_FA951B7310CA0218F506BAB16CE07368" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_63D1DE54DFAF9F7569D4BAB16CE047E2" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_FA951B7310CA0218F506BAB16CE07368" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfIncome" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_78883ADF778362D2759ADFB0A88305DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_StatementTable_78883ADF778362D2759ADFB0A88305DA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_63C8ABD065A3E5927DAFDFB0A883FC65" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_78883ADF778362D2759ADFB0A88305DA" xlink:to="loc_dei_LegalEntityAxis_63C8ABD065A3E5927DAFDFB0A883FC65" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_390B3CAB5F380B0BEAADDFB0A884AB98_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_63C8ABD065A3E5927DAFDFB0A883FC65" xlink:to="loc_dei_EntityDomain_390B3CAB5F380B0BEAADDFB0A884AB98_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_390B3CAB5F380B0BEAADDFB0A884AB98" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_63C8ABD065A3E5927DAFDFB0A883FC65" xlink:to="loc_dei_EntityDomain_390B3CAB5F380B0BEAADDFB0A884AB98" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_86C117EE78044F681263DFB0A88414DB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_390B3CAB5F380B0BEAADDFB0A884AB98" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_86C117EE78044F681263DFB0A88414DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_BC2C09E5E674DCE0485BDFB0A8848958" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_Revenues_BC2C09E5E674DCE0485BDFB0A8848958" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpensesAbstract" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingAndProductionCosts" xlink:label="loc_cmcsa_ProgrammingAndProductionCosts_F1EDA0BDE4FD3961D786DFB0A8847B5A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_cmcsa_ProgrammingAndProductionCosts_F1EDA0BDE4FD3961D786DFB0A8847B5A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherOperatingAndAdministrative" xlink:label="loc_cmcsa_OtherOperatingAndAdministrative_985565088438FBE14795DFB0A884049B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_cmcsa_OtherOperatingAndAdministrative_985565088438FBE14795DFB0A884049B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MarketingAndAdvertisingExpense" xlink:label="loc_us-gaap_MarketingAndAdvertisingExpense_6628739B46CC98DE0C18DFB0A88408D0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_us-gaap_MarketingAndAdvertisingExpense_6628739B46CC98DE0C18DFB0A88408D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_E5F1ECB70819736D34BEDFB0A88543D2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_us-gaap_Depreciation_E5F1ECB70819736D34BEDFB0A88543D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_B1DC3C136BFA7ADB57A7DFB0A8853D1B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_B1DC3C136BFA7ADB57A7DFB0A8853D1B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_FC1577911B3691A80BD2DFB0A885AF99" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_6FF382235AB658822551DFB0A884217E" xlink:to="loc_us-gaap_CostsAndExpenses_FC1577911B3691A80BD2DFB0A885AF99" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_BA908F4CEE68AA73EAA7DFB0A8851836" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_OperatingIncomeLoss_BA908F4CEE68AA73EAA7DFB0A8851836" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_6200403764E9DBA59B57DFB0A8854C72" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_InterestExpense_6200403764E9DBA59B57DFB0A8854C72" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_8922AE7C0669D5643BF0DFB0A885AD31" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_8922AE7C0669D5643BF0DFB0A885AD31" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_9BD274548267EF4FE8ECDFB0A885AB3F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_9BD274548267EF4FE8ECDFB0A885AB3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_59DC6EEB2EAD34E7476CDFB0A885B284" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_59DC6EEB2EAD34E7476CDFB0A885B284" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_66FA5533F1C5E97E3E54DFB0A8852368" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_ProfitLoss_66FA5533F1C5E97E3E54DFB0A8852368" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_5CD4239A51824F7430A3DFB0A885DB20" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_5CD4239A51824F7430A3DFB0A885DB20" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_B40A59B2F8D806228638DFB0A885A655" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_B40A59B2F8D806228638DFB0A885A655" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_3FA1823806599C6ACEFEDFB0A885608B" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_NetIncomeLoss_3FA1823806599C6ACEFEDFB0A885608B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_301835396D68A77A4FF6DFB0A8852870" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_EarningsPerShareBasic_301835396D68A77A4FF6DFB0A8852870" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_8CA5BCE8B0F10C1CF250DFB0A885288A" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_EarningsPerShareDiluted_8CA5BCE8B0F10C1CF250DFB0A885288A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_F3F9C1E5B24D50B1F21FDFB0A885A619" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_410E2899E8EBABF31776DFB0A8842326" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_F3F9C1E5B24D50B1F21FDFB0A885A619" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_5E283997D65367EBFCAFDB648BFF7260" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_5A2902DA0D5C77CF1959DB648BF9BEEF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_5E283997D65367EBFCAFDB648BFF7260" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_5A2902DA0D5C77CF1959DB648BF9BEEF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_369F08178154F583346CDB648BF9B67F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_5A2902DA0D5C77CF1959DB648BF9BEEF" xlink:to="loc_dei_LegalEntityAxis_369F08178154F583346CDB648BF9B67F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_369F08178154F583346CDB648BF9B67F" xlink:to="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_369F08178154F583346CDB648BF9B67F" xlink:to="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastHoldingsMember" xlink:label="loc_cmcsa_ComcastHoldingsMember_67AD1FC9E138EEE73024DB648BF948B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC" xlink:to="loc_cmcsa_ComcastHoldingsMember_67AD1FC9E138EEE73024DB648BF948B9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CcclParentMember" xlink:label="loc_cmcsa_CcclParentMember_D0BAA0F0DCD154C5CA00DB648BF93AFB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC" xlink:to="loc_cmcsa_CcclParentMember_D0BAA0F0DCD154C5CA00DB648BF93AFB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalMediaParentMember" xlink:label="loc_cmcsa_NbcuniversalMediaParentMember_B8C242FA7AE729CB3B06DB648BF9A283" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_34D189EC79A0C5D18D3CDB648BF994EC" xlink:to="loc_cmcsa_NbcuniversalMediaParentMember_B8C242FA7AE729CB3B06DB648BF9A283" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="loc_us-gaap_ConsolidatedEntitiesAxis_4F707E3F0B1872469841DB648BF99D63" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_5A2902DA0D5C77CF1959DB648BF9BEEF" xlink:to="loc_us-gaap_ConsolidatedEntitiesAxis_4F707E3F0B1872469841DB648BF99D63" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_4F707E3F0B1872469841DB648BF99D63" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_4F707E3F0B1872469841DB648BF99D63" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_42F4F7921D0394B1A292DB648BFA89E4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:to="loc_us-gaap_ParentCompanyMember_42F4F7921D0394B1A292DB648BFA89E4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_34BF9306D7DE1A565009DB648BFAFBC0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_34BF9306D7DE1A565009DB648BFAFBC0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuarantorSubsidiariesMember" xlink:label="loc_us-gaap_GuarantorSubsidiariesMember_1EC7736FE49DAE9F5603DB648BFADE13" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:to="loc_us-gaap_GuarantorSubsidiariesMember_1EC7736FE49DAE9F5603DB648BFADE13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_A6FB134389817C1E89DADB648BFA7B8D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C59EBA9D1C7143F19D41DB648BF958CB" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_A6FB134389817C1E89DADB648BFA7B8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_295C4B20A83BFED3F0DCDB648BFA7839" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_5A2902DA0D5C77CF1959DB648BF9BEEF" xlink:to="loc_us-gaap_ConsolidationItemsAxis_295C4B20A83BFED3F0DCDB648BFA7839" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_295C4B20A83BFED3F0DCDB648BFA7839" xlink:to="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_295C4B20A83BFED3F0DCDB648BFA7839" xlink:to="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReportableLegalEntitiesMember" xlink:label="loc_us-gaap_ReportableLegalEntitiesMember_C150AAEEFDA67D55E0E4DB648BFA6F6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0" xlink:to="loc_us-gaap_ReportableLegalEntitiesMember_C150AAEEFDA67D55E0E4DB648BFA6F6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_C2E5276667805146CCB3DB8A07683EF9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_B9366B26C6C3F30516FADB648BFADBC0" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_C2E5276667805146CCB3DB8A07683EF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_5E283997D65367EBFCAFDB648BFF7260" xlink:to="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_7C7F06282F92162E68FBDB648BFFAEA2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_7C7F06282F92162E68FBDB648BFFAEA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_47D4663617C025262C21DB648BFF4CC2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_47D4663617C025262C21DB648BFF4CC2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingRightsCurrent" xlink:label="loc_cmcsa_ProgrammingRightsCurrent_360BCD29C747DE4FA92EDB648C00D502" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_cmcsa_ProgrammingRightsCurrent_360BCD29C747DE4FA92EDB648C00D502" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="loc_us-gaap_OtherAssetsCurrent_AB4B530DBCF009ACED18DB648C000B10" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_OtherAssetsCurrent_AB4B530DBCF009ACED18DB648C000B10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_DB3FF6039C74E32BFACFDB648C00DE9C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_AssetsCurrent_DB3FF6039C74E32BFACFDB648C00DE9C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCosts" xlink:label="loc_cmcsa_FilmAndTelevisionCosts_10B20C7D940E23A1357FDB648C009C24" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_cmcsa_FilmAndTelevisionCosts_10B20C7D940E23A1357FDB648C009C24" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermInvestments" xlink:label="loc_us-gaap_LongTermInvestments_BDBAF27E2407440862DBDB648C00FCDC" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_LongTermInvestments_BDBAF27E2407440862DBDB648C00FCDC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_InvestmentsInAndAmountsDueFromSubsidiariesEliminatedUponConsolidation" xlink:label="loc_cmcsa_InvestmentsInAndAmountsDueFromSubsidiariesEliminatedUponConsolidation_807097E162AD9D1BBBBADB648C008376" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_cmcsa_InvestmentsInAndAmountsDueFromSubsidiariesEliminatedUponConsolidation_807097E162AD9D1BBBBADB648C008376" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_E64C64D86E1F612E4976DB648C005395" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_E64C64D86E1F612E4976DB648C005395" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IndefiniteLivedFranchiseRights" xlink:label="loc_us-gaap_IndefiniteLivedFranchiseRights_74D253367657BC4DF887DB648C00F714" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_IndefiniteLivedFranchiseRights_74D253367657BC4DF887DB648C00F714" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_086424B051CA590BC5AADB648C0028FD" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_Goodwill_086424B051CA590BC5AADB648C0028FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="loc_us-gaap_OtherIntangibleAssetsNet_4801598D29C34ADEDA77DB648C00F47D" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_OtherIntangibleAssetsNet_4801598D29C34ADEDA77DB648C00F47D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_7E490C25DA34DDBE35DEDB648C0017CA" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_7E490C25DA34DDBE35DEDB648C0017CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_2409FD90DA83E6683594DB648C016725" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_AD80FB3B203416A19348DB648BFFA7B9" xlink:to="loc_us-gaap_Assets_2409FD90DA83E6683594DB648C016725" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_5E283997D65367EBFCAFDB648BFF7260" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_E7A97D537C096FC2C76FDB648C01D5C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_AccountsPayableCurrent_E7A97D537C096FC2C76FDB648C01D5C7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AccruedParticipationsAndResidualsCurrent" xlink:label="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_5D0F96BD15EF5CE232B4DB648C01AC21" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_5D0F96BD15EF5CE232B4DB648C01AC21" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_6E28B35100F224295B21DB648C017B4E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_DeferredRevenueCurrent_6E28B35100F224295B21DB648C017B4E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AccruedExpensesAndOtherCurrentLiabilitiesIncludingDeferredRevenue" xlink:label="loc_cmcsa_AccruedExpensesAndOtherCurrentLiabilitiesIncludingDeferredRevenue_6916825065A8C0960C24DB648C015C5F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_cmcsa_AccruedExpensesAndOtherCurrentLiabilitiesIncludingDeferredRevenue_6916825065A8C0960C24DB648C015C5F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtCurrent" xlink:label="loc_us-gaap_DebtCurrent_FD888CBB63BE536BC235DB648C01BB47" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_DebtCurrent_FD888CBB63BE536BC235DB648C01BB47" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_36FE4D8609452EFF1CEDDB648C013CF1" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_LiabilitiesCurrent_36FE4D8609452EFF1CEDDB648C013CF1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_D82DB6BF660214C5B351DB648C01C38A" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_D82DB6BF660214C5B351DB648C01C38A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_54682EAE162E344FA853DB648C012D00" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_54682EAE162E344FA853DB648C012D00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_F2B9ED368C325CC99A4CDB648C01464B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_F2B9ED368C325CC99A4CDB648C01464B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_382ADF3B82581C493EEEDB648C018BE5" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_382ADF3B82581C493EEEDB648C018BE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_782B65A60F5AE0DE2961DB648C02C1FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:to="loc_us-gaap_CommonStockValue_782B65A60F5AE0DE2961DB648C02C1FC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherStockholdersEquity" xlink:label="loc_cmcsa_OtherStockholdersEquity_AC3682361D7DE4A6A013DB648C0294BC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:to="loc_cmcsa_OtherStockholdersEquity_AC3682361D7DE4A6A013DB648C0294BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_74626460A494324BF2F8DB648C0206B4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:to="loc_us-gaap_StockholdersEquity_74626460A494324BF2F8DB648C0206B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_4F7F5DBD8AC1F7FA1FD6DB648C021454" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:to="loc_us-gaap_MinorityInterest_4F7F5DBD8AC1F7FA1FD6DB648C021454" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_AEB86A10AA1D7DEB93FBDB648C02AFFA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_A380A8A4000E5E4E0519DB648C02A58A" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_AEB86A10AA1D7DEB93FBDB648C02AFFA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_082688D967ED799EB81FDB648C022695" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_706E679173BA4A4B270FDB648C01507C" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_082688D967ED799EB81FDB648C022695" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfCashFlowsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_A98F0BECF4F40F7A68D7DB648C227B5D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_A98F0BECF4F40F7A68D7DB648C227B5D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_CF4D52BB485BD28CAA08DB648C233985" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_A98F0BECF4F40F7A68D7DB648C227B5D" xlink:to="loc_dei_LegalEntityAxis_CF4D52BB485BD28CAA08DB648C233985" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_CF4D52BB485BD28CAA08DB648C233985" xlink:to="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_CF4D52BB485BD28CAA08DB648C233985" xlink:to="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastHoldingsMember" xlink:label="loc_cmcsa_ComcastHoldingsMember_D4FF1597AA0727D88704DB648C235BC2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3" xlink:to="loc_cmcsa_ComcastHoldingsMember_D4FF1597AA0727D88704DB648C235BC2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CcclParentMember" xlink:label="loc_cmcsa_CcclParentMember_BDAA1B18C523F4846921DB648C235835" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3" xlink:to="loc_cmcsa_CcclParentMember_BDAA1B18C523F4846921DB648C235835" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalMediaParentMember" xlink:label="loc_cmcsa_NbcuniversalMediaParentMember_0129EED89CDEEA744960DB648C2393C1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_F256E5C604252A6ED838DB648C23C3A3" xlink:to="loc_cmcsa_NbcuniversalMediaParentMember_0129EED89CDEEA744960DB648C2393C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="loc_us-gaap_ConsolidatedEntitiesAxis_16083069BEE2E8DD5494DB648C23E6FD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_A98F0BECF4F40F7A68D7DB648C227B5D" xlink:to="loc_us-gaap_ConsolidatedEntitiesAxis_16083069BEE2E8DD5494DB648C23E6FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_16083069BEE2E8DD5494DB648C23E6FD" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_16083069BEE2E8DD5494DB648C23E6FD" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_4C8A9C8920937EAA7B08DB648C2314AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:to="loc_us-gaap_ParentCompanyMember_4C8A9C8920937EAA7B08DB648C2314AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_9E8AAD7644AE7003F7A2DB648C233895" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_9E8AAD7644AE7003F7A2DB648C233895" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuarantorSubsidiariesMember" xlink:label="loc_us-gaap_GuarantorSubsidiariesMember_73BA72DC304EF9562BCBDB648C23AC49" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:to="loc_us-gaap_GuarantorSubsidiariesMember_73BA72DC304EF9562BCBDB648C23AC49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_51CE6E8A31A976D34E1EDB648C23C4C3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_81EAC012D6F3EEC569FCDB648C230091" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_51CE6E8A31A976D34E1EDB648C23C4C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_EBD67C364AEFC4FBAB5DDB648C24739E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_A98F0BECF4F40F7A68D7DB648C227B5D" xlink:to="loc_us-gaap_ConsolidationItemsAxis_EBD67C364AEFC4FBAB5DDB648C24739E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_EBD67C364AEFC4FBAB5DDB648C24739E" xlink:to="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_EBD67C364AEFC4FBAB5DDB648C24739E" xlink:to="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReportableLegalEntitiesMember" xlink:label="loc_us-gaap_ReportableLegalEntitiesMember_E28D5DA7CE2828101D27DB648C24908A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054" xlink:to="loc_us-gaap_ReportableLegalEntitiesMember_E28D5DA7CE2828101D27DB648C24908A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_E6A3D18130803EFBC0EEDB899A5B87EA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_9CC795F5DD2A187DFFB5DB648C249054" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_E6A3D18130803EFBC0EEDB899A5B87EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_66B45F4A71E74627A2E0DB648C24C058" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_66B45F4A71E74627A2E0DB648C24C058" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_767D77E0FB1639D08F01DB648C246E26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_66B45F4A71E74627A2E0DB648C24C058" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_767D77E0FB1639D08F01DB648C246E26" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NetTransactionsWithAffiliates" xlink:label="loc_cmcsa_NetTransactionsWithAffiliates_9CF9BD5913E9A9C90623DB648C24A3D1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_cmcsa_NetTransactionsWithAffiliates_9CF9BD5913E9A9C90623DB648C24A3D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_A40B7C752E1674062913DB648C2464CF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_A40B7C752E1674062913DB648C2464CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_B0AAC87C54EA93493A92DB648C249611" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_B0AAC87C54EA93493A92DB648C249611" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties" xlink:label="loc_cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties_374A44521EB3C3B2BA13DB648C24CF19" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_cmcsa_PaymentsForAcquisitionsAndConstructionOfRealEstateProperties_374A44521EB3C3B2BA13DB648C24CF19" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_9D0399771ED19C029039DB648C25D868" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_9D0399771ED19C029039DB648C25D868" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProceedsFromSalesOfBusinessesAndInvestments" xlink:label="loc_cmcsa_ProceedsFromSalesOfBusinessesAndInvestments_BDB856E08E45066F041ADB648C25B916" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_cmcsa_ProceedsFromSalesOfBusinessesAndInvestments_BDB856E08E45066F041ADB648C25B916" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_3100E89F98E354649E8DDB648C259A78" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_3100E89F98E354649E8DDB648C259A78" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_E85AA16484102541EF0DDB648C258F5A" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_E85AA16484102541EF0DDB648C258F5A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_0370DCAC05519187536CDB648C259352" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_843AE52BF633BFFDB6C3DB648C24BDAD" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_0370DCAC05519187536CDB648C259352" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromRepaymentsOfShortTermDebt" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_DFBD34FAF3D89FC35C24DB648C255FB7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_DFBD34FAF3D89FC35C24DB648C255FB7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_7DADCF07547C7DC55D19DB648C25C235" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_7DADCF07547C7DC55D19DB648C25C235" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfOtherDebt" xlink:label="loc_us-gaap_RepaymentsOfOtherDebt_402CBDA722DFA28E600CDB648C258694" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_RepaymentsOfOtherDebt_402CBDA722DFA28E600CDB648C258694" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_5EF5D4F1138858513D4EDB648C26488C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_5EF5D4F1138858513D4EDB648C26488C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDividends" xlink:label="loc_us-gaap_PaymentsOfDividends_A3C073C49DA5ACC6847EDB648C26FC4B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_PaymentsOfDividends_A3C073C49DA5ACC6847EDB648C26FC4B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock_68A64EC16882EF7B6554DB648C26CDBB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_cmcsa_DistributionsToNoncontrollingInterestsAndDividendsForRedeemableSubsidiaryPreferredStock_68A64EC16882EF7B6554DB648C26CDBB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_E0A13636E0E4D808B2D1DB648C268638" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_E0A13636E0E4D808B2D1DB648C268638" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_345C4FD2FCBEAF664879DB648C26E808" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_9C98AE5B9B54C4457F6BDB648C2501A0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_345C4FD2FCBEAF664879DB648C26E808" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_994AF1091A49C1646A65DB648C26931E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_994AF1091A49C1646A65DB648C26931E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_38D6396300045648D905DB648C262F5E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_62060A48D116C7FA610CDB648C248F18" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_38D6396300045648D905DB648C262F5E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationCondensedConsolidatingStatementOfIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_F33B45562188F18AAB63E3803DF90F32" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_F33B45562188F18AAB63E3803DF90F32" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_37B12DEE5F9CCF5EB9CDE3803DF9E3D2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_F33B45562188F18AAB63E3803DF90F32" xlink:to="loc_dei_LegalEntityAxis_37B12DEE5F9CCF5EB9CDE3803DF9E3D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_37B12DEE5F9CCF5EB9CDE3803DF9E3D2" xlink:to="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_37B12DEE5F9CCF5EB9CDE3803DF9E3D2" xlink:to="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastHoldingsMember" xlink:label="loc_cmcsa_ComcastHoldingsMember_A01A0D0C10496B8D432DE3803DFACCB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20" xlink:to="loc_cmcsa_ComcastHoldingsMember_A01A0D0C10496B8D432DE3803DFACCB5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CcclParentMember" xlink:label="loc_cmcsa_CcclParentMember_DB6FAF0AB8DD7B9A327BE3803DFAFEBE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20" xlink:to="loc_cmcsa_CcclParentMember_DB6FAF0AB8DD7B9A327BE3803DFAFEBE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalMediaParentMember" xlink:label="loc_cmcsa_NbcuniversalMediaParentMember_239AB29CF1CE88A4F51AE3803DFAC67C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6291304529D8F35D8D1EE3803DFA2B20" xlink:to="loc_cmcsa_NbcuniversalMediaParentMember_239AB29CF1CE88A4F51AE3803DFAC67C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="loc_us-gaap_ConsolidatedEntitiesAxis_050D1C687577BE6DE487E3803DFBB76A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_F33B45562188F18AAB63E3803DF90F32" xlink:to="loc_us-gaap_ConsolidatedEntitiesAxis_050D1C687577BE6DE487E3803DFBB76A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_050D1C687577BE6DE487E3803DFBB76A" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_050D1C687577BE6DE487E3803DFBB76A" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_A5FCAA7743BFA27CFCB8E3803DFB43C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:to="loc_us-gaap_ParentCompanyMember_A5FCAA7743BFA27CFCB8E3803DFB43C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_994BBC01902A13E3CE53E3803DFB12B3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_994BBC01902A13E3CE53E3803DFB12B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuarantorSubsidiariesMember" xlink:label="loc_us-gaap_GuarantorSubsidiariesMember_A1F6614442510F560C05E3803DFBC8C3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:to="loc_us-gaap_GuarantorSubsidiariesMember_A1F6614442510F560C05E3803DFBC8C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_B495630947C8C8901E6CE3803DFB3763" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_C69DDE0D734ABD190D9CE3803DFB4AA0" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_B495630947C8C8901E6CE3803DFB3763" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_9792059C7DD4A17A7C61E3803DFC9116" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_F33B45562188F18AAB63E3803DF90F32" xlink:to="loc_us-gaap_ConsolidationItemsAxis_9792059C7DD4A17A7C61E3803DFC9116" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_9792059C7DD4A17A7C61E3803DFC9116" xlink:to="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_9792059C7DD4A17A7C61E3803DFC9116" xlink:to="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReportableLegalEntitiesMember" xlink:label="loc_us-gaap_ReportableLegalEntitiesMember_4CB9FE357C5271795F4EE3803DFCC49C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49" xlink:to="loc_us-gaap_ReportableLegalEntitiesMember_4CB9FE357C5271795F4EE3803DFCC49C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_9641EFA5354A9E0089D4E3803DFC0D1E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_832D8220916D42895712E3803DFC4B49" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_9641EFA5354A9E0089D4E3803DFC0D1E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaap_RevenuesAbstract_6BE61C8D2B2276F83CD9E3803DFC4CA8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_RevenuesAbstract_6BE61C8D2B2276F83CD9E3803DFC4CA8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SalesRevenueServicesNet" xlink:label="loc_us-gaap_SalesRevenueServicesNet_4002A553418C0F042896E3803DFD654B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_6BE61C8D2B2276F83CD9E3803DFC4CA8" xlink:to="loc_us-gaap_SalesRevenueServicesNet_4002A553418C0F042896E3803DFD654B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ManagementFeesRevenue" xlink:label="loc_us-gaap_ManagementFeesRevenue_3BF65A772CAE4120A56DE3803DFD581C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_6BE61C8D2B2276F83CD9E3803DFC4CA8" xlink:to="loc_us-gaap_ManagementFeesRevenue_3BF65A772CAE4120A56DE3803DFD581C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_5D5161A6E75135535A0AE3803DFD8F70" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_6BE61C8D2B2276F83CD9E3803DFC4CA8" xlink:to="loc_us-gaap_Revenues_5D5161A6E75135535A0AE3803DFD8F70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpensesAbstract" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingAndProductionCosts" xlink:label="loc_cmcsa_ProgrammingAndProductionCosts_02B4FAC30701F5F719BDE3803DFD7E64" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_cmcsa_ProgrammingAndProductionCosts_02B4FAC30701F5F719BDE3803DFD7E64" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherOperatingAndAdministrative" xlink:label="loc_cmcsa_OtherOperatingAndAdministrative_0F539AC6CFE4B2D0886CE3803DFE5514" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_cmcsa_OtherOperatingAndAdministrative_0F539AC6CFE4B2D0886CE3803DFE5514" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MarketingAndAdvertisingExpense" xlink:label="loc_us-gaap_MarketingAndAdvertisingExpense_8D626B44A83CE3734351E3803DFE4AB0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_us-gaap_MarketingAndAdvertisingExpense_8D626B44A83CE3734351E3803DFE4AB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_60375C40E060A189C1F3E3803DFE9F79" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_us-gaap_Depreciation_60375C40E060A189C1F3E3803DFE9F79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_157A007CF56C1D743BA6E3803DFEB15B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_157A007CF56C1D743BA6E3803DFEB15B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_5E7DE5D5070F3B5FC1DEE3803DFE4E16" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_787DABA16E4232C6D874E3803DFD3633" xlink:to="loc_us-gaap_CostsAndExpenses_5E7DE5D5070F3B5FC1DEE3803DFE4E16" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_5E460B2DC712D1FDB694E3803DFF5103" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_OperatingIncomeLoss_5E460B2DC712D1FDB694E3803DFF5103" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_B21B984D7C17748E9D14E3803DFF8803" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_InterestExpense_B21B984D7C17748E9D14E3803DFF8803" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_C12FD7C141DE668D6EEDE3803DFFFE0D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_C12FD7C141DE668D6EEDE3803DFFFE0D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_D0FD4D850F4F8E7536C3E3803DFF8C69" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_D0FD4D850F4F8E7536C3E3803DFF8C69" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_DEFC716D2A982DDCAFD0E3803DFFF62A" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_DEFC716D2A982DDCAFD0E3803DFFF62A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_3807FB3FC262A84DB7FCE3803DFF720C" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_ProfitLoss_3807FB3FC262A84DB7FCE3803DFF720C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_660356E0E41E4C7F02DEE3803DFFCE95" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_cmcsa_NetIncomeLossAttributableToNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStock_660356E0E41E4C7F02DEE3803DFFCE95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_7725923B1B044C7EF666E3803E0127EA" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_NetIncomeLoss_7725923B1B044C7EF666E3803E0127EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_8436E8E09545124EA613E3803E013BC9" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_4F269C60F0A66B074242E3803DFC2441" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_8436E8E09545124EA613E3803E013BC9" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_A518B96F25764A9DE66F2B60E25F321B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:to="loc_us-gaap_DebtInstrumentTable_A518B96F25764A9DE66F2B60E25F321B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_78370E6F88CE8B09B6432B60E25F0455" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_A518B96F25764A9DE66F2B60E25F321B" xlink:to="loc_us-gaap_DebtInstrumentAxis_78370E6F88CE8B09B6432B60E25F0455" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_78370E6F88CE8B09B6432B60E25F0455" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_78370E6F88CE8B09B6432B60E25F0455" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SeniorNotesMember" xlink:label="loc_us-gaap_SeniorNotesMember_0B2850A065E5709AA2142B60E25F7647" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:to="loc_us-gaap_SeniorNotesMember_0B2850A065E5709AA2142B60E25F7647" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalEnterpriseCreditFacilityMember" xlink:label="loc_cmcsa_NbcuniversalEnterpriseCreditFacilityMember_0369B9794DEFAC9C77232B60E25F29E2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:to="loc_cmcsa_NbcuniversalEnterpriseCreditFacilityMember_0369B9794DEFAC9C77232B60E25F29E2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_UniversalStudiosJapanTermLoanMaturingMarch2022Member" xlink:label="loc_cmcsa_UniversalStudiosJapanTermLoanMaturingMarch2022Member_879AC1CE2A5F1522F06C2B60E25F4707" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:to="loc_cmcsa_UniversalStudiosJapanTermLoanMaturingMarch2022Member_879AC1CE2A5F1522F06C2B60E25F4707" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastHoldingsZonesDueOctober2029Member" xlink:label="loc_cmcsa_ComcastHoldingsZonesDueOctober2029Member_A183DD22F27477379E7A2B60E25F6E3C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:to="loc_cmcsa_ComcastHoldingsZonesDueOctober2029Member_A183DD22F27477379E7A2B60E25F6E3C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastHoldingsZonesDueNovember2029Member" xlink:label="loc_cmcsa_ComcastHoldingsZonesDueNovember2029Member_E11F160F351E4BC0C5502B60E25FA129" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F0877DE3B4C93F92349E2B60E25FC866" xlink:to="loc_cmcsa_ComcastHoldingsZonesDueNovember2029Member_E11F160F351E4BC0C5502B60E25FA129" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GuaranteeObligationsCurrentPrincipalBalance" xlink:label="loc_cmcsa_GuaranteeObligationsCurrentPrincipalBalance_FA9EABD52ED3C6BD14DB2B60E25F823D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:to="loc_cmcsa_GuaranteeObligationsCurrentPrincipalBalance_FA9EABD52ED3C6BD14DB2B60E25F823D" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GuaranteeObligationsLineOfCreditFacility" xlink:label="loc_cmcsa_GuaranteeObligationsLineOfCreditFacility_55619C9018D54F3B34AF2B60E25FC48F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:to="loc_cmcsa_GuaranteeObligationsLineOfCreditFacility_55619C9018D54F3B34AF2B60E25FC48F" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GuaranteeObligationsTermLoans" xlink:label="loc_cmcsa_GuaranteeObligationsTermLoans_A74072F67CAF8469A1F32B60E25F724E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:to="loc_cmcsa_GuaranteeObligationsTermLoans_A74072F67CAF8469A1F32B60E25F724E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NonGuaranteeObligationsCurrentPrincipalBalance" xlink:label="loc_cmcsa_NonGuaranteeObligationsCurrentPrincipalBalance_7B987718051A922E30312B60E25F4D85" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_CBD78AD13C649D80109B2B60E25F9EA7" xlink:to="loc_cmcsa_NonGuaranteeObligationsCurrentPrincipalBalance_7B987718051A922E30312B60E25F4D85" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatingFinancialInformationTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DocumentAndEntityInformationLineItems" xlink:label="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DocumentAndEntityInformationTable" xlink:label="loc_cmcsa_DocumentAndEntityInformationTable_36880455FDC7520881F1BA2E8F082569" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_cmcsa_DocumentAndEntityInformationTable_36880455FDC7520881F1BA2E8F082569" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_D949562874205BDCAB456E0267ADAC12" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_DocumentAndEntityInformationTable_36880455FDC7520881F1BA2E8F082569" xlink:to="loc_us-gaap_StatementClassOfStockAxis_D949562874205BDCAB456E0267ADAC12" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_C29945B0194F1CCD82C95B0BC4934436_D061F302BD365E8AB8056ABF43058F3B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D949562874205BDCAB456E0267ADAC12" xlink:to="loc_us-gaap_ClassOfStockDomain_C29945B0194F1CCD82C95B0BC4934436_D061F302BD365E8AB8056ABF43058F3B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_6D41C81354C7532F82811DD49A30A82D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D949562874205BDCAB456E0267ADAC12" xlink:to="loc_us-gaap_ClassOfStockDomain_6D41C81354C7532F82811DD49A30A82D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_B9F9B1414A5D527CA8C12030D25E0E48" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6D41C81354C7532F82811DD49A30A82D" xlink:to="loc_us-gaap_CommonClassAMember_B9F9B1414A5D527CA8C12030D25E0E48" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_BA6C59B38CA45EE7BF8EDD61393383F0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6D41C81354C7532F82811DD49A30A82D" xlink:to="loc_us-gaap_CommonClassBMember_BA6C59B38CA45EE7BF8EDD61393383F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_73EA3DEFA5ED5DFD9D31B11D9659AA61" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_DocumentAndEntityInformationTable_36880455FDC7520881F1BA2E8F082569" xlink:to="loc_dei_LegalEntityAxis_73EA3DEFA5ED5DFD9D31B11D9659AA61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_8CE020640B6C6EFA9D295B0BC49324A7_D061F302BD365E8AB8056ABF43058F3B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_73EA3DEFA5ED5DFD9D31B11D9659AA61" xlink:to="loc_dei_EntityDomain_8CE020640B6C6EFA9D295B0BC49324A7_D061F302BD365E8AB8056ABF43058F3B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9637EEE7B48D5D09806FDFAA9D9F4029" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_73EA3DEFA5ED5DFD9D31B11D9659AA61" xlink:to="loc_dei_EntityDomain_9637EEE7B48D5D09806FDFAA9D9F4029" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_A240EFF245075553A5207FD69CF41B05" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9637EEE7B48D5D09806FDFAA9D9F4029" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_A240EFF245075553A5207FD69CF41B05" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_23A1DEE26B8050EBA077DA816401B2C3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_EntityRegistrantName_23A1DEE26B8050EBA077DA816401B2C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_573DC4E72CD75B02AE09C7DC48B57929" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_EntityCentralIndexKey_573DC4E72CD75B02AE09C7DC48B57929" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_TradingSymbol" xlink:label="loc_dei_TradingSymbol_31C8A351E2875FBD95B5A609884F2E1A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_TradingSymbol_31C8A351E2875FBD95B5A609884F2E1A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_0227F9E6902155E3952117DE8E9AEAC5" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_CurrentFiscalYearEndDate_0227F9E6902155E3952117DE8E9AEAC5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_9695F983D9785DD8A5A3A7850B14B80C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_EntityFilerCategory_9695F983D9785DD8A5A3A7850B14B80C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_27042B0B3FD15470AD294935661FFAEE" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_DocumentType_27042B0B3FD15470AD294935661FFAEE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_530B0767F1B5519BAB6EBB7A6C7AEFF8" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_DocumentPeriodEndDate_530B0767F1B5519BAB6EBB7A6C7AEFF8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_17509AF47AAC5955AFA867442E175462" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_DocumentFiscalYearFocus_17509AF47AAC5955AFA867442E175462" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_C2085A4088FB5480BAC6A4C2342C4E98" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_DocumentFiscalPeriodFocus_C2085A4088FB5480BAC6A4C2342C4E98" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_25C21B9322A356108AA18B5E54B40151" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_AmendmentFlag_25C21B9322A356108AA18B5E54B40151" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_D32A91B405415433B50E4CA2014CFDD2" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_15D0DE155EED52B0A71B9BB40A019901" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_D32A91B405415433B50E4CA2014CFDD2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShareDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/FilmAndTelevisionCosts" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostLineItems" xlink:label="loc_cmcsa_FilmAndTelevisionCostLineItems_93C9DB29BB471427C5ECFC1E36E9A7F8" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostTable" xlink:label="loc_cmcsa_FilmAndTelevisionCostTable_2B7488C0FC8F1F202D52FC1E36E965ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_93C9DB29BB471427C5ECFC1E36E9A7F8" xlink:to="loc_cmcsa_FilmAndTelevisionCostTable_2B7488C0FC8F1F202D52FC1E36E965ED" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_184A22876BE01D2EE00BFC1E36E9AD3E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_FilmAndTelevisionCostTable_2B7488C0FC8F1F202D52FC1E36E965ED" xlink:to="loc_dei_LegalEntityAxis_184A22876BE01D2EE00BFC1E36E9AD3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E9F10A2BE7A315CF5F6FFC1E36E9DED4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_184A22876BE01D2EE00BFC1E36E9AD3E" xlink:to="loc_dei_EntityDomain_E9F10A2BE7A315CF5F6FFC1E36E9DED4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E9F10A2BE7A315CF5F6FFC1E36E9DED4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_184A22876BE01D2EE00BFC1E36E9AD3E" xlink:to="loc_dei_EntityDomain_E9F10A2BE7A315CF5F6FFC1E36E9DED4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_17F4D298EF2FF4443F98FC1E36E95D93" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E9F10A2BE7A315CF5F6FFC1E36E9DED4" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_17F4D298EF2FF4443F98FC1E36E95D93" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostsDisclosureTextBlock" xlink:label="loc_cmcsa_FilmAndTelevisionCostsDisclosureTextBlock_E17165922378F9B7B8D8FC1E36E9BA86" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_93C9DB29BB471427C5ECFC1E36E9A7F8" xlink:to="loc_cmcsa_FilmAndTelevisionCostsDisclosureTextBlock_E17165922378F9B7B8D8FC1E36E9BA86" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/FilmAndTelevisionCostsFilmAndTelevisionCostsdetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostLineItems" xlink:label="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostTable" xlink:label="loc_cmcsa_FilmAndTelevisionCostTable_53AD028B95968C694BB0FC1E36E2BEC7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_cmcsa_FilmAndTelevisionCostTable_53AD028B95968C694BB0FC1E36E2BEC7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_FEE520891128DB09CD3BFC1E36E28FB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_FilmAndTelevisionCostTable_53AD028B95968C694BB0FC1E36E2BEC7" xlink:to="loc_dei_LegalEntityAxis_FEE520891128DB09CD3BFC1E36E28FB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_ABC5E8ACD701CE63BFB6FC1E36E30804_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_FEE520891128DB09CD3BFC1E36E28FB0" xlink:to="loc_dei_EntityDomain_ABC5E8ACD701CE63BFB6FC1E36E30804_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_ABC5E8ACD701CE63BFB6FC1E36E30804" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_FEE520891128DB09CD3BFC1E36E28FB0" xlink:to="loc_dei_EntityDomain_ABC5E8ACD701CE63BFB6FC1E36E30804" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_F695C263575667D326BEFC1E36E394DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ABC5E8ACD701CE63BFB6FC1E36E30804" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_F695C263575667D326BEFC1E36E394DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TheatricalFilmCostsAbstract" xlink:label="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TheatricalFilmCostsReleased" xlink:label="loc_us-gaap_TheatricalFilmCostsReleased_A978DE76D8DA6AFD23D9FC1E36E3DC24" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:to="loc_us-gaap_TheatricalFilmCostsReleased_A978DE76D8DA6AFD23D9FC1E36E3DC24" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TheatricalFilmCostsCompletedAndNotReleased" xlink:label="loc_us-gaap_TheatricalFilmCostsCompletedAndNotReleased_0C6A96736AF0846E8FA4FC1E36E37A74" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:to="loc_us-gaap_TheatricalFilmCostsCompletedAndNotReleased_0C6A96736AF0846E8FA4FC1E36E37A74" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_TheatricalFilmCostsInProductionAndInDevelopment" xlink:label="loc_cmcsa_TheatricalFilmCostsInProductionAndInDevelopment_EA8E696522C144B0737DFC1E36E38D39" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:to="loc_cmcsa_TheatricalFilmCostsInProductionAndInDevelopment_EA8E696522C144B0737DFC1E36E38D39" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TheatricalFilmCosts" xlink:label="loc_us-gaap_TheatricalFilmCosts_BE588494D1C8F75B16C1FC1E36E3E55D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TheatricalFilmCostsAbstract_58C189B612BF56E41F16FC1E36E3AEE0" xlink:to="loc_us-gaap_TheatricalFilmCosts_BE588494D1C8F75B16C1FC1E36E3E55D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DirectToTelevisionFilmCostsAbstract" xlink:label="loc_us-gaap_DirectToTelevisionFilmCostsAbstract_A32922A02A3D8DD646CFFC1E36E32A57" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_us-gaap_DirectToTelevisionFilmCostsAbstract_A32922A02A3D8DD646CFFC1E36E32A57" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DirectToTelevisionFilmCostsReleased" xlink:label="loc_us-gaap_DirectToTelevisionFilmCostsReleased_1AE2D0A4942929323015FC1E36E3CC51" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DirectToTelevisionFilmCostsAbstract_A32922A02A3D8DD646CFFC1E36E32A57" xlink:to="loc_us-gaap_DirectToTelevisionFilmCostsReleased_1AE2D0A4942929323015FC1E36E3CC51" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DirecttoTelevisionFilmCostsInProductionandInDevelopment" xlink:label="loc_cmcsa_DirecttoTelevisionFilmCostsInProductionandInDevelopment_21197E9AB37341D1AED6FC1E36E36651" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DirectToTelevisionFilmCostsAbstract_A32922A02A3D8DD646CFFC1E36E32A57" xlink:to="loc_cmcsa_DirecttoTelevisionFilmCostsInProductionandInDevelopment_21197E9AB37341D1AED6FC1E36E36651" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DirectToTelevisionFilmCosts" xlink:label="loc_us-gaap_DirectToTelevisionFilmCosts_954BC193587B6D5F5BAEFC1E36E389D3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DirectToTelevisionFilmCostsAbstract_A32922A02A3D8DD646CFFC1E36E32A57" xlink:to="loc_us-gaap_DirectToTelevisionFilmCosts_954BC193587B6D5F5BAEFC1E36E389D3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingRightsLessAmortization" xlink:label="loc_cmcsa_ProgrammingRightsLessAmortization_8EB064C67F70E2C631B8FC1E36E365A1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_cmcsa_ProgrammingRightsLessAmortization_8EB064C67F70E2C631B8FC1E36E365A1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_TotalFilmAndTelevisionCostsAndProgrammingRightsAfterAmortization" xlink:label="loc_cmcsa_TotalFilmAndTelevisionCostsAndProgrammingRightsAfterAmortization_381ECFFC4531A29F1066FC1E36E3C983" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_cmcsa_TotalFilmAndTelevisionCostsAndProgrammingRightsAfterAmortization_381ECFFC4531A29F1066FC1E36E3C983" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ProgrammingRightsCurrent" xlink:label="loc_cmcsa_ProgrammingRightsCurrent_798BA5F0527453B54059FC1E36E3343D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_cmcsa_ProgrammingRightsCurrent_798BA5F0527453B54059FC1E36E3343D" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCosts" xlink:label="loc_cmcsa_FilmAndTelevisionCosts_B242FBD4832F019C18E9FC1E36E3E143" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_24E4F6FB03C6F7EA57F9FC1E36E37BA0" xlink:to="loc_cmcsa_FilmAndTelevisionCosts_B242FBD4832F019C18E9FC1E36E3E143" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/FilmAndTelevisionCostsTables" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostLineItems" xlink:label="loc_cmcsa_FilmAndTelevisionCostLineItems_68709C5DAAA301F4FB44FC7AEFF82096" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCostTable" xlink:label="loc_cmcsa_FilmAndTelevisionCostTable_AB48F0BD7F1689D3F13DFC7AEFF2D3EF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_68709C5DAAA301F4FB44FC7AEFF82096" xlink:to="loc_cmcsa_FilmAndTelevisionCostTable_AB48F0BD7F1689D3F13DFC7AEFF2D3EF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_EB8A3AF6F7A4738C8383FC7AEFF73D5A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_FilmAndTelevisionCostTable_AB48F0BD7F1689D3F13DFC7AEFF2D3EF" xlink:to="loc_dei_LegalEntityAxis_EB8A3AF6F7A4738C8383FC7AEFF73D5A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4AF3544422561B621128FC7AEFF7FD16_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_EB8A3AF6F7A4738C8383FC7AEFF73D5A" xlink:to="loc_dei_EntityDomain_4AF3544422561B621128FC7AEFF7FD16_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4AF3544422561B621128FC7AEFF7FD16" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_EB8A3AF6F7A4738C8383FC7AEFF73D5A" xlink:to="loc_dei_EntityDomain_4AF3544422561B621128FC7AEFF7FD16" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_23504BF8922C0FC29C72FC7AEFF88A6C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_4AF3544422561B621128FC7AEFF7FD16" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_23504BF8922C0FC29C72FC7AEFF88A6C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ScheduleOfFilmAndTelevisionCostsTableTextBlock" xlink:label="loc_cmcsa_ScheduleOfFilmAndTelevisionCostsTableTextBlock_B888E31F2E6C377EB5B9FC7AEFF8F161" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_FilmAndTelevisionCostLineItems_68709C5DAAA301F4FB44FC7AEFF82096" xlink:to="loc_cmcsa_ScheduleOfFilmAndTelevisionCostsTableTextBlock_B888E31F2E6C377EB5B9FC7AEFF8F161" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/Investments" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_InvestmentsLineItems" xlink:label="loc_cmcsa_InvestmentsLineItems_08201094D3972AAD20FDF3D841139CB3" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_InvestmentsTable" xlink:label="loc_cmcsa_InvestmentsTable_8189DE4E1F610C78387EF3D84113192C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_InvestmentsLineItems_08201094D3972AAD20FDF3D841139CB3" xlink:to="loc_cmcsa_InvestmentsTable_8189DE4E1F610C78387EF3D84113192C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_39CD502289BEF20E5CCAF3D84113184B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_InvestmentsTable_8189DE4E1F610C78387EF3D84113192C" xlink:to="loc_dei_LegalEntityAxis_39CD502289BEF20E5CCAF3D84113184B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_99B65980A37254DAD710F3D8411305C5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_39CD502289BEF20E5CCAF3D84113184B" xlink:to="loc_dei_EntityDomain_99B65980A37254DAD710F3D8411305C5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_99B65980A37254DAD710F3D8411305C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_39CD502289BEF20E5CCAF3D84113184B" xlink:to="loc_dei_EntityDomain_99B65980A37254DAD710F3D8411305C5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_101AD29394CE1664ABC5F3D841132231" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_99B65980A37254DAD710F3D8411305C5" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_101AD29394CE1664ABC5F3D841132231" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:label="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_22D0069E1563F9716F22F3D84113CD6E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_InvestmentsLineItems_08201094D3972AAD20FDF3D841139CB3" xlink:to="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_22D0069E1563F9716F22F3D84113CD6E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsEquityMethodDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_BEEBA8074297194E46ACF3520DBF1DBF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_BEEBA8074297194E46ACF3520DBF1DBF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_23F57222F7E4836165DEF3520DBF1C05" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_BEEBA8074297194E46ACF3520DBF1DBF" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_23F57222F7E4836165DEF3520DBF1C05" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_23F57222F7E4836165DEF3520DBF1C05" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_23F57222F7E4836165DEF3520DBF1C05" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AtairosMember" xlink:label="loc_cmcsa_AtairosMember_B8BC57E64692B1FD906BF3520DCE0DE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF" xlink:to="loc_cmcsa_AtairosMember_B8BC57E64692B1FD906BF3520DCE0DE9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_HuluMember" xlink:label="loc_cmcsa_HuluMember_F7A5776386B40E56C396F3520DCE02CF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF" xlink:to="loc_cmcsa_HuluMember_F7A5776386B40E56C396F3520DCE02CF" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_WeatherChannelMember" xlink:label="loc_cmcsa_WeatherChannelMember_3EF2C45BB89FDE3B4DC2F3520DCE9EDB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_7DA10C1D645D0F46A04AF3520DCEA7AF" xlink:to="loc_cmcsa_WeatherChannelMember_3EF2C45BB89FDE3B4DC2F3520DCE9EDB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_4255E07EC69FEFCB68C8F3520DCE37E9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_BEEBA8074297194E46ACF3520DBF1DBF" xlink:to="loc_dei_LegalEntityAxis_4255E07EC69FEFCB68C8F3520DCE37E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4D0C44ABFB8856FB4BD0F3520DCEB589_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4255E07EC69FEFCB68C8F3520DCE37E9" xlink:to="loc_dei_EntityDomain_4D0C44ABFB8856FB4BD0F3520DCEB589_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4D0C44ABFB8856FB4BD0F3520DCEB589" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4255E07EC69FEFCB68C8F3520DCE37E9" xlink:to="loc_dei_EntityDomain_4D0C44ABFB8856FB4BD0F3520DCEB589" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_FC6E94CC7F25EE8B8485F3520DCE452C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_4D0C44ABFB8856FB4BD0F3520DCEB589" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_FC6E94CC7F25EE8B8485F3520DCE452C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquityMethodInvestmentFundingCommitment" xlink:label="loc_cmcsa_EquityMethodInvestmentFundingCommitment_D4555B4794CEA11A713CF3520DCE7A00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_cmcsa_EquityMethodInvestmentFundingCommitment_D4555B4794CEA11A713CF3520DCE7A00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestments" xlink:label="loc_us-gaap_EquityMethodInvestments_0D58DCC0D8B21B4B3507F3520DCEC2F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_us-gaap_EquityMethodInvestments_0D58DCC0D8B21B4B3507F3520DCEC2F7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CapitalContributionToVIE" xlink:label="loc_cmcsa_CapitalContributionToVIE_E1C69C2EDC641AD9A9FAF3520DCE787C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_cmcsa_CapitalContributionToVIE_E1C69C2EDC641AD9A9FAF3520DCE787C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_56978B812E145F61B2F7F3520DCE8A47" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_56978B812E145F61B2F7F3520DCE8A47" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquityMethodInvestmentCapitalContribution" xlink:label="loc_cmcsa_EquityMethodInvestmentCapitalContribution_CB7D5A83A0A734DEA8F5F3520DCEB686" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_cmcsa_EquityMethodInvestmentCapitalContribution_CB7D5A83A0A734DEA8F5F3520DCEB686" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal" xlink:label="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_616410A60FFCC97AACE9F3520DCEB3DA" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_342BD2453577A635D592F3520DCE20C7" xlink:to="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_616410A60FFCC97AACE9F3520DCEB3DA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems" xlink:label="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable" xlink:label="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_87582BE7580818A2CD00F822B4DADE39" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:to="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_87582BE7580818A2CD00F822B4DADE39" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_87890D0E038CEE90B847F822B4DA94DC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_87582BE7580818A2CD00F822B4DADE39" xlink:to="loc_dei_LegalEntityAxis_87890D0E038CEE90B847F822B4DA94DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_80BBAC75E5E80BF58094F822B4DA1029_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_87890D0E038CEE90B847F822B4DA94DC" xlink:to="loc_dei_EntityDomain_80BBAC75E5E80BF58094F822B4DA1029_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_80BBAC75E5E80BF58094F822B4DA1029" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_87890D0E038CEE90B847F822B4DA94DC" xlink:to="loc_dei_EntityDomain_80BBAC75E5E80BF58094F822B4DA1029" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_B7411EA728583A9532B0F822B4DAF9BD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_80BBAC75E5E80BF58094F822B4DA1029" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_B7411EA728583A9532B0F822B4DAF9BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_F01C0995033A23237E77F822B4DB60D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_F01C0995033A23237E77F822B4DB60D9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquitySecuritiesFvNiGainLoss" xlink:label="loc_cmcsa_EquitySecuritiesFvNiGainLoss_66C631ACEBD073256A84F822B4DB97BB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:to="loc_cmcsa_EquitySecuritiesFvNiGainLoss_66C631ACEBD073256A84F822B4DB97BB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherIncomeLossNet" xlink:label="loc_cmcsa_OtherIncomeLossNet_F92A0C9CB35F57E2F784F822B4DB981F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:to="loc_cmcsa_OtherIncomeLossNet_F92A0C9CB35F57E2F784F822B4DB981F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_00AEFB2935335BFD02A2F822B4DB7A26" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_4889BFE853A5E29D0A39F822B4DAB22D" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_00AEFB2935335BFD02A2F822B4DB7A26" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsMarketableEquitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ScheduleofFairValueMethodInvestmentsLineItems" xlink:label="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ScheduleofFairValueMethodInvestmentsTable" xlink:label="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_49C97BD26EE42A18CE12F3D7D4B4405F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:to="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_49C97BD26EE42A18CE12F3D7D4B4405F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_45CBBC6CC5400BFF8085F3D7D4B47F71" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_49C97BD26EE42A18CE12F3D7D4B4405F" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_45CBBC6CC5400BFF8085F3D7D4B47F71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_F4FAA1DDCDE566B558A7F3D7D4B45FA5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_45CBBC6CC5400BFF8085F3D7D4B47F71" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_F4FAA1DDCDE566B558A7F3D7D4B45FA5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_F4FAA1DDCDE566B558A7F3D7D4B45FA5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_45CBBC6CC5400BFF8085F3D7D4B47F71" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_F4FAA1DDCDE566B558A7F3D7D4B45FA5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SnapMember" xlink:label="loc_cmcsa_SnapMember_C145C82D4858A1AB831AF3D7D4B4A81D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_F4FAA1DDCDE566B558A7F3D7D4B45FA5" xlink:to="loc_cmcsa_SnapMember_C145C82D4858A1AB831AF3D7D4B4A81D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_C1FE1580F556D8F88D33F3D7D4B4B381" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_49C97BD26EE42A18CE12F3D7D4B4405F" xlink:to="loc_dei_LegalEntityAxis_C1FE1580F556D8F88D33F3D7D4B4B381" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9AE76E3EFA1BF60D81C8F3D7D4B40430_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_C1FE1580F556D8F88D33F3D7D4B4B381" xlink:to="loc_dei_EntityDomain_9AE76E3EFA1BF60D81C8F3D7D4B40430_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9AE76E3EFA1BF60D81C8F3D7D4B40430" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_C1FE1580F556D8F88D33F3D7D4B4B381" xlink:to="loc_dei_EntityDomain_9AE76E3EFA1BF60D81C8F3D7D4B40430" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_3413E335504DEE22576BF3D7D4B4C992" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9AE76E3EFA1BF60D81C8F3D7D4B40430" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_3413E335504DEE22576BF3D7D4B4C992" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireMarketableSecurities" xlink:label="loc_us-gaap_PaymentsToAcquireMarketableSecurities_77718186F96489346EBFF3D7D4B431F1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:to="loc_us-gaap_PaymentsToAcquireMarketableSecurities_77718186F96489346EBFF3D7D4B431F1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_MemberContribution" xlink:label="loc_cmcsa_MemberContribution_7AF8C3E4156E03B10A02F3D7D4B4EEE3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:to="loc_cmcsa_MemberContribution_7AF8C3E4156E03B10A02F3D7D4B4EEE3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquitySecuritiesFVNI" xlink:label="loc_cmcsa_EquitySecuritiesFVNI_8A1632E5E9453B73016CF3D7D4B4683C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:to="loc_cmcsa_EquitySecuritiesFVNI_8A1632E5E9453B73016CF3D7D4B4683C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquitySecuritiesFVNIUnrealizedGain" xlink:label="loc_cmcsa_EquitySecuritiesFVNIUnrealizedGain_A2867D6E1AF6EF0EFBF7F3D7D4B437C3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_72E5FAE866FBAED1DFB1F3D7D4B41BB3" xlink:to="loc_cmcsa_EquitySecuritiesFVNIUnrealizedGain_A2867D6E1AF6EF0EFBF7F3D7D4B437C3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsOtherInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCostMethodInvestmentsLineItems" xlink:label="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCostMethodInvestmentsTable" xlink:label="loc_us-gaap_ScheduleOfCostMethodInvestmentsTable_1D45154F0AD162174922F3D84029B284" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:to="loc_us-gaap_ScheduleOfCostMethodInvestmentsTable_1D45154F0AD162174922F3D84029B284" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_892ED434A7AB0A2BD945F3D840293D0E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsTable_1D45154F0AD162174922F3D84029B284" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_892ED434A7AB0A2BD945F3D840293D0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_76B04611D01B4FDE4DB3F3D840297FA6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_892ED434A7AB0A2BD945F3D840293D0E" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_76B04611D01B4FDE4DB3F3D840297FA6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_76B04611D01B4FDE4DB3F3D840297FA6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_892ED434A7AB0A2BD945F3D840293D0E" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_76B04611D01B4FDE4DB3F3D840297FA6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AirTouchMember" xlink:label="loc_cmcsa_AirTouchMember_F48F754626CD746EB04DF3D8402944C6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_76B04611D01B4FDE4DB3F3D840297FA6" xlink:to="loc_cmcsa_AirTouchMember_F48F754626CD746EB04DF3D8402944C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_82E0B979CB7C0D578F49F3D84029A244" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsTable_1D45154F0AD162174922F3D84029B284" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_82E0B979CB7C0D578F49F3D84029A244" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4E358A2BCC4E3AEC1D17F3D840298A2E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_82E0B979CB7C0D578F49F3D84029A244" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4E358A2BCC4E3AEC1D17F3D840298A2E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4E358A2BCC4E3AEC1D17F3D840298A2E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_82E0B979CB7C0D578F49F3D84029A244" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4E358A2BCC4E3AEC1D17F3D840298A2E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_69AE49B66BD99713DC90F3D840299C88" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4E358A2BCC4E3AEC1D17F3D840298A2E" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_69AE49B66BD99713DC90F3D840299C88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_5C7A453E55BEC8924B29F3D840297331" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsTable_1D45154F0AD162174922F3D84029B284" xlink:to="loc_dei_LegalEntityAxis_5C7A453E55BEC8924B29F3D840297331" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3F24EE7DC404EF650FB0F3D8402971A3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5C7A453E55BEC8924B29F3D840297331" xlink:to="loc_dei_EntityDomain_3F24EE7DC404EF650FB0F3D8402971A3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3F24EE7DC404EF650FB0F3D8402971A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5C7A453E55BEC8924B29F3D840297331" xlink:to="loc_dei_EntityDomain_3F24EE7DC404EF650FB0F3D8402971A3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AirTouchMember" xlink:label="loc_cmcsa_AirTouchMember_2680ED90B42ED31B62FDF3D84029E23C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3F24EE7DC404EF650FB0F3D8402971A3" xlink:to="loc_cmcsa_AirTouchMember_2680ED90B42ED31B62FDF3D84029E23C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NumberofPreferredStockSeries" xlink:label="loc_cmcsa_NumberofPreferredStockSeries_F6642964FBEEC2EC160CF3D840295B2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:to="loc_cmcsa_NumberofPreferredStockSeries_F6642964FBEEC2EC160CF3D840295B2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesNoncurrent" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesNoncurrent_7CAC2BBBE8451274F649F3D84029F38D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesNoncurrent_7CAC2BBBE8451274F649F3D84029F38D" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FairValueOfRedeemablePreferredShares" xlink:label="loc_cmcsa_FairValueOfRedeemablePreferredShares_2D237C18194800C063CFF3D84029C2F4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:to="loc_cmcsa_FairValueOfRedeemablePreferredShares_2D237C18194800C063CFF3D84029C2F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesFairValue" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_DAAFFC537DDEE7324DFEF3EA650EF738" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCostMethodInvestmentsLineItems_F69F3FF80254D180AA75F3D84029C30A" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_DAAFFC537DDEE7324DFEF3EA650EF738" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsScheduleOfInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems" xlink:label="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable" xlink:label="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_0235DBD695F64FE0CA63F822B4E8E55C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_0235DBD695F64FE0CA63F822B4E8E55C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1A4844BA772819DD061DF822B4E86B22" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNITable_0235DBD695F64FE0CA63F822B4E8E55C" xlink:to="loc_dei_LegalEntityAxis_1A4844BA772819DD061DF822B4E86B22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0955E330F0194989E64DF822B4E9C8C9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1A4844BA772819DD061DF822B4E86B22" xlink:to="loc_dei_EntityDomain_0955E330F0194989E64DF822B4E9C8C9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0955E330F0194989E64DF822B4E9C8C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1A4844BA772819DD061DF822B4E86B22" xlink:to="loc_dei_EntityDomain_0955E330F0194989E64DF822B4E9C8C9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_B2FFCA039001E88279FEF822B4E98E72" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0955E330F0194989E64DF822B4E9C8C9" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_B2FFCA039001E88279FEF822B4E98E72" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvestments" xlink:label="loc_us-gaap_EquityMethodInvestments_EFACEBD073A101379173F822B4EAD841" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_us-gaap_EquityMethodInvestments_EFACEBD073A101379173F822B4EAD841" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquitySecuritiesFVNI" xlink:label="loc_cmcsa_EquitySecuritiesFVNI_515FAFB16E731F317641F822B4EA0AD2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_cmcsa_EquitySecuritiesFVNI_515FAFB16E731F317641F822B4EA0AD2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount" xlink:label="loc_cmcsa_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_AC0A3FF1E6BC82E6E1B5F822B4EAC9CF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_cmcsa_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_AC0A3FF1E6BC82E6E1B5F822B4EAC9CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_B898963352C4FCDAA765F822B4EAA90A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_us-gaap_OtherInvestments_B898963352C4FCDAA765F822B4EAA90A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_D0DBE9807EC12EEF7273F822B4EA22F5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_us-gaap_Investments_D0DBE9807EC12EEF7273F822B4EA22F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_F69F8708A1827F1A49B5F822B4EB6457" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_us-gaap_ShortTermInvestments_F69F8708A1827F1A49B5F822B4EB6457" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermInvestments" xlink:label="loc_us-gaap_LongTermInvestments_4B5D0DE369D894E32FFFF822B4EBFA39" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DebtSecuritiesTradingandEquitySecuritiesFVNILineItems_2F87E3C03589EDC9C8FAF822B4E9379A" xlink:to="loc_us-gaap_LongTermInvestments_4B5D0DE369D894E32FFFF822B4EBFA39" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsTables" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_InvestmentsLineItems" xlink:label="loc_cmcsa_InvestmentsLineItems_99DA7CFD89C06AF775ECF822B4F4B779" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_InvestmentsTable" xlink:label="loc_cmcsa_InvestmentsTable_62F21D17EB0A11AC274AF822B4F3CEDA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_InvestmentsLineItems_99DA7CFD89C06AF775ECF822B4F4B779" xlink:to="loc_cmcsa_InvestmentsTable_62F21D17EB0A11AC274AF822B4F3CEDA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_C8793DE4D9C3ED1A5408F822B4F324A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_InvestmentsTable_62F21D17EB0A11AC274AF822B4F3CEDA" xlink:to="loc_dei_LegalEntityAxis_C8793DE4D9C3ED1A5408F822B4F324A8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E6297E6B260C9081B931F822B4F378B4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_C8793DE4D9C3ED1A5408F822B4F324A8" xlink:to="loc_dei_EntityDomain_E6297E6B260C9081B931F822B4F378B4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E6297E6B260C9081B931F822B4F378B4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_C8793DE4D9C3ED1A5408F822B4F324A8" xlink:to="loc_dei_EntityDomain_E6297E6B260C9081B931F822B4F378B4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_4144B7E6C0994304A3D2F822B4F33CE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E6297E6B260C9081B931F822B4F378B4" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_4144B7E6C0994304A3D2F822B4F33CE8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SummaryInvestmentHoldingsTextBlock" xlink:label="loc_us-gaap_SummaryInvestmentHoldingsTextBlock_2041F02ED15109FAB3A1F822B4F4E1D6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_InvestmentsLineItems_99DA7CFD89C06AF775ECF822B4F4B779" xlink:to="loc_us-gaap_SummaryInvestmentHoldingsTextBlock_2041F02ED15109FAB3A1F822B4F4E1D6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComponentsOfInvestmentandOtherIncomeLossNetTableTextBlock" xlink:label="loc_cmcsa_ComponentsOfInvestmentandOtherIncomeLossNetTableTextBlock_6BC7903764DCF5C79513F822B4F475BB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_InvestmentsLineItems_99DA7CFD89C06AF775ECF822B4F4B779" xlink:to="loc_cmcsa_ComponentsOfInvestmentandOtherIncomeLossNetTableTextBlock_6BC7903764DCF5C79513F822B4F475BB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebt" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_347B95C8785D09D0D100FC1E37444DAD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_30ED3AA94B40BC80F590FC1E3744BB07" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_347B95C8785D09D0D100FC1E37444DAD" xlink:to="loc_us-gaap_DebtInstrumentTable_30ED3AA94B40BC80F590FC1E3744BB07" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_78059281DA807CBD04A2FC1E3744DA7D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30ED3AA94B40BC80F590FC1E3744BB07" xlink:to="loc_dei_LegalEntityAxis_78059281DA807CBD04A2FC1E3744DA7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_BCF738A17172CCED2C4BFC1E37445F1A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_78059281DA807CBD04A2FC1E3744DA7D" xlink:to="loc_dei_EntityDomain_BCF738A17172CCED2C4BFC1E37445F1A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_BCF738A17172CCED2C4BFC1E37445F1A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_78059281DA807CBD04A2FC1E3744DA7D" xlink:to="loc_dei_EntityDomain_BCF738A17172CCED2C4BFC1E37445F1A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_68203B3257FFB3F14135FC1E3744573C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_BCF738A17172CCED2C4BFC1E37445F1A" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_68203B3257FFB3F14135FC1E3744573C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_EA529BD32CB4BD0F8D36FC1E37455B9E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_347B95C8785D09D0D100FC1E37444DAD" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_EA529BD32CB4BD0F8D36FC1E37455B9E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtCommercialPaperProgramsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermDebtLineItems" xlink:label="loc_us-gaap_ShortTermDebtLineItems_3EE369E9B3FDE770B9343FCB05E9E7E7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShortTermDebtTable" xlink:label="loc_us-gaap_ScheduleOfShortTermDebtTable_9B042F7F45687CC8EC683FCB05E94309" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortTermDebtLineItems_3EE369E9B3FDE770B9343FCB05E9E7E7" xlink:to="loc_us-gaap_ScheduleOfShortTermDebtTable_9B042F7F45687CC8EC683FCB05E94309" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_9CD8A8B7132A719B29C83FCB05E9A793" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable_9B042F7F45687CC8EC683FCB05E94309" xlink:to="loc_us-gaap_CreditFacilityAxis_9CD8A8B7132A719B29C83FCB05E9A793" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_AC0158C712161B1AE6543FCB05E9AA26_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_9CD8A8B7132A719B29C83FCB05E9A793" xlink:to="loc_us-gaap_CreditFacilityDomain_AC0158C712161B1AE6543FCB05E9AA26_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_AC0158C712161B1AE6543FCB05E9AA26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_9CD8A8B7132A719B29C83FCB05E9A793" xlink:to="loc_us-gaap_CreditFacilityDomain_AC0158C712161B1AE6543FCB05E9AA26" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_4D79C64ED8BA4A56B6873FCB05E98FDA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_AC0158C712161B1AE6543FCB05E9AA26" xlink:to="loc_us-gaap_CommercialPaperMember_4D79C64ED8BA4A56B6873FCB05E98FDA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_4DF4E68E5327E689FE033FCB05E9FD86" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable_9B042F7F45687CC8EC683FCB05E94309" xlink:to="loc_dei_LegalEntityAxis_4DF4E68E5327E689FE033FCB05E9FD86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_23CC6C316FE8394BD74A3FCB05E9511A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4DF4E68E5327E689FE033FCB05E9FD86" xlink:to="loc_dei_EntityDomain_23CC6C316FE8394BD74A3FCB05E9511A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_23CC6C316FE8394BD74A3FCB05E9511A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4DF4E68E5327E689FE033FCB05E9FD86" xlink:to="loc_dei_EntityDomain_23CC6C316FE8394BD74A3FCB05E9511A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalEnterpriseMember" xlink:label="loc_cmcsa_NbcuniversalEnterpriseMember_D454A2832077877678F23FCB05E9B25B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_23CC6C316FE8394BD74A3FCB05E9511A" xlink:to="loc_cmcsa_NbcuniversalEnterpriseMember_D454A2832077877678F23FCB05E9B25B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaper" xlink:label="loc_us-gaap_CommercialPaper_FB74424F6AFA122E36D33FCB05E9FC8F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_3EE369E9B3FDE770B9343FCB05E9E7E7" xlink:to="loc_us-gaap_CommercialPaper_FB74424F6AFA122E36D33FCB05E9FC8F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtCrossGuaranteeStructureDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_2C71E5371261ED45B3FDF2C39B2A3900" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:to="loc_dei_LegalEntityAxis_2C71E5371261ED45B3FDF2C39B2A3900" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7483ACC1B41F162579ECF2C39B2A2FDD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_2C71E5371261ED45B3FDF2C39B2A3900" xlink:to="loc_dei_EntityDomain_7483ACC1B41F162579ECF2C39B2A2FDD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7483ACC1B41F162579ECF2C39B2A2FDD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_2C71E5371261ED45B3FDF2C39B2A3900" xlink:to="loc_dei_EntityDomain_7483ACC1B41F162579ECF2C39B2A2FDD" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_83832FF58A43C1140A09F2C39B2AE80C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7483ACC1B41F162579ECF2C39B2A2FDD" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_83832FF58A43C1140A09F2C39B2AE80C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_9EE62952C8EFCF9FCD0EF2C39B2A4773" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:to="loc_us-gaap_CreditFacilityAxis_9EE62952C8EFCF9FCD0EF2C39B2A4773" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_66F4D7A732897EF1FC4DF2C39B2A99F8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_9EE62952C8EFCF9FCD0EF2C39B2A4773" xlink:to="loc_us-gaap_CreditFacilityDomain_66F4D7A732897EF1FC4DF2C39B2A99F8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_66F4D7A732897EF1FC4DF2C39B2A99F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_9EE62952C8EFCF9FCD0EF2C39B2A4773" xlink:to="loc_us-gaap_CreditFacilityDomain_66F4D7A732897EF1FC4DF2C39B2A99F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_361D539DC8276D3C349FF2C39B2A13B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_66F4D7A732897EF1FC4DF2C39B2A99F8" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_361D539DC8276D3C349FF2C39B2A13B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_5E9E594BDE3B8D3AE8E7F2C39B2A0BB6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:to="loc_us-gaap_DebtInstrumentAxis_5E9E594BDE3B8D3AE8E7F2C39B2A0BB6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_AC379A50C49B493E3BD7F2C39B2AC9CE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_5E9E594BDE3B8D3AE8E7F2C39B2A0BB6" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_AC379A50C49B493E3BD7F2C39B2AC9CE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_AC379A50C49B493E3BD7F2C39B2AC9CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_5E9E594BDE3B8D3AE8E7F2C39B2A0BB6" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_AC379A50C49B493E3BD7F2C39B2AC9CE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastAndComcastCableDebtSecuritiesMember" xlink:label="loc_cmcsa_ComcastAndComcastCableDebtSecuritiesMember_D5B62C5F0CA893001FF5F2C39B2A0EFA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_AC379A50C49B493E3BD7F2C39B2AC9CE" xlink:to="loc_cmcsa_ComcastAndComcastCableDebtSecuritiesMember_D5B62C5F0CA893001FF5F2C39B2A0EFA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis_7E0A9DA713FA2599B02DF2C39B2A8F10" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_F943109AF6D2DD8CA86CF2C39B2A7DB5" xlink:to="loc_us-gaap_CounterpartyNameAxis_7E0A9DA713FA2599B02DF2C39B2A8F10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_98358AB5C3913EEE89B0F2C39B2A03A7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CounterpartyNameAxis_7E0A9DA713FA2599B02DF2C39B2A8F10" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_98358AB5C3913EEE89B0F2C39B2A03A7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_98358AB5C3913EEE89B0F2C39B2A03A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis_7E0A9DA713FA2599B02DF2C39B2A8F10" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_98358AB5C3913EEE89B0F2C39B2A03A7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalEnterpriseMember" xlink:label="loc_cmcsa_NbcuniversalEnterpriseMember_E04571080FE377088056F2C39B2A9FEA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_98358AB5C3913EEE89B0F2C39B2A03A7" xlink:to="loc_cmcsa_NbcuniversalEnterpriseMember_E04571080FE377088056F2C39B2A9FEA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OwnershipInCableHoldingCompanySubsidiaries" xlink:label="loc_cmcsa_OwnershipInCableHoldingCompanySubsidiaries_B07DE9757491C1FF87E3F2C39B2A2E91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_OwnershipInCableHoldingCompanySubsidiaries_B07DE9757491C1FF87E3F2C39B2A2E91" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GuaranteeObligationsMaximumCapacityOfCreditFacility" xlink:label="loc_cmcsa_GuaranteeObligationsMaximumCapacityOfCreditFacility_1958C75A3113B0590983F2C39B2ADD32" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_GuaranteeObligationsMaximumCapacityOfCreditFacility_1958C75A3113B0590983F2C39B2ADD32" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_GuaranteeObligationsCurrentPrincipalBalance" xlink:label="loc_cmcsa_GuaranteeObligationsCurrentPrincipalBalance_50F15756CB776119C280F2C39B2A17B4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_GuaranteeObligationsCurrentPrincipalBalance_50F15756CB776119C280F2C39B2A17B4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RelatedPartyAggregatePrincipalAmountSeniorNotesNotSubjectToGuarantee" xlink:label="loc_cmcsa_RelatedPartyAggregatePrincipalAmountSeniorNotesNotSubjectToGuarantee_80793872DD414DEA53EAF2C39B2A9F35" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_RelatedPartyAggregatePrincipalAmountSeniorNotesNotSubjectToGuarantee_80793872DD414DEA53EAF2C39B2A9F35" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RelatedPartyCreditFacilityNotSubjectToGuarantee" xlink:label="loc_cmcsa_RelatedPartyCreditFacilityNotSubjectToGuarantee_DDA49355EB57C062748FF2C39B2A185A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_RelatedPartyCreditFacilityNotSubjectToGuarantee_DDA49355EB57C062748FF2C39B2A185A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RelatedPartyLiquidationPreferencePreferredStockNotSubjectToGuarantee" xlink:label="loc_cmcsa_RelatedPartyLiquidationPreferencePreferredStockNotSubjectToGuarantee_0DFD34F7C96DBE2D5233F2C39B2A0768" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_36AAEF892071610E1469F2C39B2A50DE" xlink:to="loc_cmcsa_RelatedPartyLiquidationPreferencePreferredStockNotSubjectToGuarantee_0DFD34F7C96DBE2D5233F2C39B2A0768" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtDebtBorrowingsdetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_E886440D339998609969DEB84C9194E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:to="loc_us-gaap_DebtInstrumentTable_E886440D339998609969DEB84C9194E0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_073898E089FAB239AA83DEB84C91410B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_E886440D339998609969DEB84C9194E0" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_073898E089FAB239AA83DEB84C91410B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_55DEA1D2BBED2BE7933CDEB84C915886_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_073898E089FAB239AA83DEB84C91410B" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_55DEA1D2BBED2BE7933CDEB84C915886_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_55DEA1D2BBED2BE7933CDEB84C915886" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_073898E089FAB239AA83DEB84C91410B" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_55DEA1D2BBED2BE7933CDEB84C915886" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SeniorNotesMember" xlink:label="loc_us-gaap_SeniorNotesMember_9F52CD98BD7359290F2EDEB84C916309" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_55DEA1D2BBED2BE7933CDEB84C915886" xlink:to="loc_us-gaap_SeniorNotesMember_9F52CD98BD7359290F2EDEB84C916309" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_3AB5F89CE12E34AB7E15DEB84C910C7C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_E886440D339998609969DEB84C9194E0" xlink:to="loc_us-gaap_DebtInstrumentAxis_3AB5F89CE12E34AB7E15DEB84C910C7C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_3AB5F89CE12E34AB7E15DEB84C910C7C" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_3AB5F89CE12E34AB7E15DEB84C910C7C" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Senior3.90NotesDue2038Member" xlink:label="loc_cmcsa_Senior3.90NotesDue2038Member_04223D579E8BD1D4A2AADEB84C91D1A1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:to="loc_cmcsa_Senior3.90NotesDue2038Member_04223D579E8BD1D4A2AADEB84C91D1A1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Senior3.55NotesDue2028Member" xlink:label="loc_cmcsa_Senior3.55NotesDue2028Member_533887D7F8181BC17267DEB84C914E49" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:to="loc_cmcsa_Senior3.55NotesDue2028Member_533887D7F8181BC17267DEB84C914E49" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Senior4.00NotesDue2048Member" xlink:label="loc_cmcsa_Senior4.00NotesDue2048Member_70ED96D3ED9251155E46DEB84C913FA0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:to="loc_cmcsa_Senior4.00NotesDue2048Member_70ED96D3ED9251155E46DEB84C913FA0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Senior4.25NotesDue2053Member" xlink:label="loc_cmcsa_Senior4.25NotesDue2053Member_3E30890DA71A3D9DC9B6DEB84C9119F1" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:to="loc_cmcsa_Senior4.25NotesDue2053Member_3E30890DA71A3D9DC9B6DEB84C9119F1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherBorrowingsMember" xlink:label="loc_cmcsa_OtherBorrowingsMember_36F1494E3C77D0C0F394DEB84C91EBE3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7DA4C1ED603030085CF1DEB84C9132F7" xlink:to="loc_cmcsa_OtherBorrowingsMember_36F1494E3C77D0C0F394DEB84C91EBE3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_09FEFE16CFD6D403923FDEB84C914864" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_09FEFE16CFD6D403923FDEB84C914864" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtInstrumentUnamortizedDiscountPremiumNetandOtherBorrowings" xlink:label="loc_cmcsa_DebtInstrumentUnamortizedDiscountPremiumNetandOtherBorrowings_F0FDC7BC317816EB7694DEB84C914EFF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:to="loc_cmcsa_DebtInstrumentUnamortizedDiscountPremiumNetandOtherBorrowings_F0FDC7BC317816EB7694DEB84C914EFF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_3E12703BB3408365C7CFDEB84C9185B1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_3E12703BB3408365C7CFDEB84C9185B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_CC0DDDCDD9BF883E72F9DEB84C91DAEF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_BC389296DBB17562C91ADEB84C911B77" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_CC0DDDCDD9BF883E72F9DEB84C91DAEF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtDebtRepaymentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_D80D07C72474CB56857DF2C39EDDF4C5" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_AFE88205CBF7B2079D29F2C39ECD0B39" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_D80D07C72474CB56857DF2C39EDDF4C5" xlink:to="loc_us-gaap_StatementTable_AFE88205CBF7B2079D29F2C39ECD0B39" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_8E2A68FBFA07D831EDD6F2C39ECD5A08" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AFE88205CBF7B2079D29F2C39ECD0B39" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_8E2A68FBFA07D831EDD6F2C39ECD5A08" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_9765927812AB2D1F96B7F2C39ECD8B49_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8E2A68FBFA07D831EDD6F2C39ECD5A08" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_9765927812AB2D1F96B7F2C39ECD8B49_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_9765927812AB2D1F96B7F2C39ECD8B49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8E2A68FBFA07D831EDD6F2C39ECD5A08" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_9765927812AB2D1F96B7F2C39ECD8B49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_BDAA5778DA608D25F89EF2C39ECD994D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_9765927812AB2D1F96B7F2C39ECD8B49" xlink:to="loc_us-gaap_SubsequentEventMember_BDAA5778DA608D25F89EF2C39ECD994D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_1F2DD4C907337839E705F2C39ECD2034" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AFE88205CBF7B2079D29F2C39ECD0B39" xlink:to="loc_us-gaap_DebtInstrumentAxis_1F2DD4C907337839E705F2C39ECD2034" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1F2DD4C907337839E705F2C39ECD2034" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1F2DD4C907337839E705F2C39ECD2034" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniveralEnterpriseSeniorFloatingRateNotesDue2018Member" xlink:label="loc_cmcsa_NBCUniveralEnterpriseSeniorFloatingRateNotesDue2018Member_D56F7D181A0BB1145247F2C39ECDC427" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:to="loc_cmcsa_NBCUniveralEnterpriseSeniorFloatingRateNotesDue2018Member_D56F7D181A0BB1145247F2C39ECDC427" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalEnterpriseSenior1.662NotesDue2018Member" xlink:label="loc_cmcsa_NBCUniversalEnterpriseSenior1.662NotesDue2018Member_4C62F7165B233264BBF1F2C39ECD9457" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:to="loc_cmcsa_NBCUniversalEnterpriseSenior1.662NotesDue2018Member_4C62F7165B233264BBF1F2C39ECD9457" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Senior5.875NotesDue2018Member" xlink:label="loc_cmcsa_Senior5.875NotesDue2018Member_0AB09116E8FA8EB284B1F2C39ECD3151" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:to="loc_cmcsa_Senior5.875NotesDue2018Member_0AB09116E8FA8EB284B1F2C39ECD3151" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherLongTermDebtMember" xlink:label="loc_cmcsa_OtherLongTermDebtMember_474312DB97D3C9505132F2C39ECDD43F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_F33ECD442B57673EB848F2C39ECD4689" xlink:to="loc_cmcsa_OtherLongTermDebtMember_474312DB97D3C9505132F2C39ECDD43F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_700853EE5139A80EE8FEF2C39ECD05E1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AFE88205CBF7B2079D29F2C39ECD0B39" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_700853EE5139A80EE8FEF2C39ECD05E1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_C9467E6826D893E95C77F2C39ECD4D99_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_700853EE5139A80EE8FEF2C39ECD05E1" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_C9467E6826D893E95C77F2C39ECD4D99_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_C9467E6826D893E95C77F2C39ECD4D99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_700853EE5139A80EE8FEF2C39ECD05E1" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_C9467E6826D893E95C77F2C39ECD4D99" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SeniorNotesMember" xlink:label="loc_us-gaap_SeniorNotesMember_5DF56B68B6BC941672E3F2C39EDD38F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_C9467E6826D893E95C77F2C39ECD4D99" xlink:to="loc_us-gaap_SeniorNotesMember_5DF56B68B6BC941672E3F2C39EDD38F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfOtherDebt" xlink:label="loc_us-gaap_RepaymentsOfOtherDebt_1761FC14A060086EDF11F2C39EDD2CE6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_D80D07C72474CB56857DF2C39EDDF4C5" xlink:to="loc_us-gaap_RepaymentsOfOtherDebt_1761FC14A060086EDF11F2C39EDD2CE6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_E2842D8711A49C8A5AA1F2C39EDDDB66" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_D80D07C72474CB56857DF2C39EDDF4C5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_E2842D8711A49C8A5AA1F2C39EDDDB66" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_4682EA8928E44FD7F0900B77893CE7CD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_4AD4580D9C54792E274A0B77893C6CB4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4682EA8928E44FD7F0900B77893CE7CD" xlink:to="loc_us-gaap_DebtInstrumentTable_4AD4580D9C54792E274A0B77893C6CB4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_EE65569E176A64A1D74D0B77893C1339" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_4AD4580D9C54792E274A0B77893C6CB4" xlink:to="loc_dei_LegalEntityAxis_EE65569E176A64A1D74D0B77893C1339" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DB0BC4C278CC206AF9AF0B77893C9182_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_EE65569E176A64A1D74D0B77893C1339" xlink:to="loc_dei_EntityDomain_DB0BC4C278CC206AF9AF0B77893C9182_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DB0BC4C278CC206AF9AF0B77893C9182" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_EE65569E176A64A1D74D0B77893C1339" xlink:to="loc_dei_EntityDomain_DB0BC4C278CC206AF9AF0B77893C9182" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_1F288AE98DD35B291D1F0B77893C9A8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DB0BC4C278CC206AF9AF0B77893C9182" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_1F288AE98DD35B291D1F0B77893C9A8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_F9D0D96282B701900AE40B77893C4581" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4682EA8928E44FD7F0900B77893CE7CD" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_F9D0D96282B701900AE40B77893C4581" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtFairValue" xlink:label="loc_us-gaap_LongTermDebtFairValue_17A8A443E5B8523281940B77893C3732" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4682EA8928E44FD7F0900B77893CE7CD" xlink:to="loc_us-gaap_LongTermDebtFairValue_17A8A443E5B8523281940B77893C3732" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtRevolvingCreditFacilitiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_D69BBFF91630A56EF141E38BAF814B15" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_92E1F3585FBCF121011EE38BAF7F719C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_D69BBFF91630A56EF141E38BAF814B15" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_92E1F3585FBCF121011EE38BAF7F719C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_4A2A2C41ABB40031B30DE38BAF808C0C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_92E1F3585FBCF121011EE38BAF7F719C" xlink:to="loc_us-gaap_CreditFacilityAxis_4A2A2C41ABB40031B30DE38BAF808C0C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_926A8CF2E89AA37B7B5CE38BAF80B7AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_4A2A2C41ABB40031B30DE38BAF808C0C" xlink:to="loc_us-gaap_CreditFacilityDomain_926A8CF2E89AA37B7B5CE38BAF80B7AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_926A8CF2E89AA37B7B5CE38BAF80B7AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_4A2A2C41ABB40031B30DE38BAF808C0C" xlink:to="loc_us-gaap_CreditFacilityDomain_926A8CF2E89AA37B7B5CE38BAF80B7AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_B9B69821C45059AA0AA7E38BAF80E2D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_926A8CF2E89AA37B7B5CE38BAF80B7AF" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_B9B69821C45059AA0AA7E38BAF80E2D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_287620F6BCEC26B96478E38BAF803F66" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_92E1F3585FBCF121011EE38BAF7F719C" xlink:to="loc_dei_LegalEntityAxis_287620F6BCEC26B96478E38BAF803F66" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_06370E4E992E7822C5F2E38BAF804866_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_287620F6BCEC26B96478E38BAF803F66" xlink:to="loc_dei_EntityDomain_06370E4E992E7822C5F2E38BAF804866_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_06370E4E992E7822C5F2E38BAF804866" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_287620F6BCEC26B96478E38BAF803F66" xlink:to="loc_dei_EntityDomain_06370E4E992E7822C5F2E38BAF804866" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NbcuniversalEnterpriseMember" xlink:label="loc_cmcsa_NbcuniversalEnterpriseMember_A64780458D7027BA5C7EE38BAF8029F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_06370E4E992E7822C5F2E38BAF804866" xlink:to="loc_cmcsa_NbcuniversalEnterpriseMember_A64780458D7027BA5C7EE38BAF8029F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_1C2621C31861A7F9E7AFE38BAF819CF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_D69BBFF91630A56EF141E38BAF814B15" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_1C2621C31861A7F9E7AFE38BAF819CF5" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_C836E5D9B5F7D6F1AEB168C185E5F15E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_197D96C17FDC25349A0368C185E05BB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_C836E5D9B5F7D6F1AEB168C185E5F15E" xlink:to="loc_us-gaap_StatementTable_197D96C17FDC25349A0368C185E05BB5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_7EE8E28F73C22038086068C185E0EAB6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_197D96C17FDC25349A0368C185E05BB5" xlink:to="loc_dei_LegalEntityAxis_7EE8E28F73C22038086068C185E0EAB6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E35CA847AB4A73DF1EBE68C185E0C44C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_7EE8E28F73C22038086068C185E0EAB6" xlink:to="loc_dei_EntityDomain_E35CA847AB4A73DF1EBE68C185E0C44C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E35CA847AB4A73DF1EBE68C185E0C44C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_7EE8E28F73C22038086068C185E0EAB6" xlink:to="loc_dei_EntityDomain_E35CA847AB4A73DF1EBE68C185E0C44C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_D8FF2E7CE7ABFCB04A1168C185E5F3E8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E35CA847AB4A73DF1EBE68C185E0C44C" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_D8FF2E7CE7ABFCB04A1168C185E5F3E8" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtBorrowingsTableTextBlock" xlink:label="loc_cmcsa_DebtBorrowingsTableTextBlock_8F6CD590F1C13C0C7C7B68C185E521BE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C836E5D9B5F7D6F1AEB168C185E5F15E" xlink:to="loc_cmcsa_DebtBorrowingsTableTextBlock_8F6CD590F1C13C0C7C7B68C185E521BE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DebtRepaymentsAndRepurchasesTableTextBlock" xlink:label="loc_cmcsa_DebtRepaymentsAndRepurchasesTableTextBlock_8CF533B5F1AB2502975768CF539AEBAB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C836E5D9B5F7D6F1AEB168C185E5F15E" xlink:to="loc_cmcsa_DebtRepaymentsAndRepurchasesTableTextBlock_8CF533B5F1AB2502975768CF539AEBAB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReform" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1AA71B466BD5983E12A662FC1106DD81" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4588D8BA3B0E6250EFD662FC11067D1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1AA71B466BD5983E12A662FC1106DD81" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4588D8BA3B0E6250EFD662FC11067D1D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_2CBF619030FDB2705D8B62FC1106F9A1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_4588D8BA3B0E6250EFD662FC11067D1D" xlink:to="loc_dei_LegalEntityAxis_2CBF619030FDB2705D8B62FC1106F9A1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D92730FA42612AA1503862FC1106BE20_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_2CBF619030FDB2705D8B62FC1106F9A1" xlink:to="loc_dei_EntityDomain_D92730FA42612AA1503862FC1106BE20_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D92730FA42612AA1503862FC1106BE20" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_2CBF619030FDB2705D8B62FC1106F9A1" xlink:to="loc_dei_EntityDomain_D92730FA42612AA1503862FC1106BE20" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_88F54DA3ED1333E4B2AF62FC11065E21" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D92730FA42612AA1503862FC1106BE20" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_88F54DA3ED1333E4B2AF62FC11065E21" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:label="loc_us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_AC8A35FC8C7C3B39F39D62FC110775FF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1AA71B466BD5983E12A662FC1106DD81" xlink:to="loc_us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_AC8A35FC8C7C3B39F39D62FC110775FF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionCableCommunicationsSegmentDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_8A1C4EBB5E2978175127BBD4EDB8150D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_8A1C4EBB5E2978175127BBD4EDB8150D" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_5A0F7E0F047FD0205AECBBDF861F6F61" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:to="loc_us-gaap_StatementScenarioAxis_5A0F7E0F047FD0205AECBBDF861F6F61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_5A0F7E0F047FD0205AECBBDF861F6F61" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_5A0F7E0F047FD0205AECBBDF861F6F61" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioPreviouslyReportedMember" xlink:label="loc_us-gaap_ScenarioPreviouslyReportedMember_FC06BC11797B54FC40F2BBDFA6912272" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D" xlink:to="loc_us-gaap_ScenarioPreviouslyReportedMember_FC06BC11797B54FC40F2BBDFA6912272" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestatementAdjustmentMember" xlink:label="loc_us-gaap_RestatementAdjustmentMember_84481BB8EB22F219CF79BBDFC8121E83" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_502DE19DD788BE3CB4B9BBDF8621DC6D" xlink:to="loc_us-gaap_RestatementAdjustmentMember_84481BB8EB22F219CF79BBDFC8121E83" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_7986EF9B49F949A6D378BBD4EDB7030F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_7986EF9B49F949A6D378BBD4EDB7030F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_6E85A4A2A6DBACF13F6DBBD4EDB76F91_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_7986EF9B49F949A6D378BBD4EDB7030F" xlink:to="loc_us-gaap_TypeOfAdoptionMember_6E85A4A2A6DBACF13F6DBBD4EDB76F91_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_6E85A4A2A6DBACF13F6DBBD4EDB76F91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_7986EF9B49F949A6D378BBD4EDB7030F" xlink:to="loc_us-gaap_TypeOfAdoptionMember_6E85A4A2A6DBACF13F6DBBD4EDB76F91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_B9F55EC80AC6EB1DBF50BBD4EDB7766F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_6E85A4A2A6DBACF13F6DBBD4EDB76F91" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_B9F55EC80AC6EB1DBF50BBD4EDB7766F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_8B70E4C134B28967CC36BBD4EDB87D35" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:to="loc_us-gaap_ProductOrServiceAxis_8B70E4C134B28967CC36BBD4EDB87D35" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_8B70E4C134B28967CC36BBD4EDB87D35" xlink:to="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_8B70E4C134B28967CC36BBD4EDB87D35" xlink:to="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialVideoMember" xlink:label="loc_cmcsa_ResidentialVideoMember_B3C6F138132ACE7AF9BEBBD4EDB8CF66" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_ResidentialVideoMember_B3C6F138132ACE7AF9BEBBD4EDB8CF66" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialHighSpeedInternetMember" xlink:label="loc_cmcsa_ResidentialHighSpeedInternetMember_21484F74868FB5F6DA6CBBD4EDB812D5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_ResidentialHighSpeedInternetMember_21484F74868FB5F6DA6CBBD4EDB812D5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialVoiceMember" xlink:label="loc_cmcsa_ResidentialVoiceMember_24A03574399D3F09A627BBD4EDB88C55" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_ResidentialVoiceMember_24A03574399D3F09A627BBD4EDB88C55" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessServicesMember" xlink:label="loc_cmcsa_BusinessServicesMember_DAF641CF202CB6EBC1BDBBD4EDB84328" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_BusinessServicesMember_DAF641CF202CB6EBC1BDBBD4EDB84328" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AdvertisingMember" xlink:label="loc_cmcsa_AdvertisingMember_EBB1A6ADEC468AFB804EBBD4EDB87066" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_AdvertisingMember_EBB1A6ADEC468AFB804EBBD4EDB87066" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherMember" xlink:label="loc_cmcsa_OtherMember_22DCE0639C56A27CEEBFBBD4EDB8AB25" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_75C13012183025F96387BBD4EDB8BE8E" xlink:to="loc_cmcsa_OtherMember_22DCE0639C56A27CEEBFBBD4EDB8AB25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_A970DBF1CC2F42FC90FDBBD4EDB84531" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_F0C5ECEBE56A0B447D7EBBD4EDB7D4B4" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_A970DBF1CC2F42FC90FDBBD4EDB84531" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_5BAE11BF3A61853DED10BBD4EDB8B733_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_A970DBF1CC2F42FC90FDBBD4EDB84531" xlink:to="loc_us-gaap_SegmentDomain_5BAE11BF3A61853DED10BBD4EDB8B733_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_5BAE11BF3A61853DED10BBD4EDB8B733" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_A970DBF1CC2F42FC90FDBBD4EDB84531" xlink:to="loc_us-gaap_SegmentDomain_5BAE11BF3A61853DED10BBD4EDB8B733" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_15CBC568836B9EEB6F9CBBD4EDB8458E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_5BAE11BF3A61853DED10BBD4EDB8B733" xlink:to="loc_cmcsa_CableCommunicationsMember_15CBC568836B9EEB6F9CBBD4EDB8458E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_47F8029DCC7401FF3B05BBD4EDB8C71B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_8A1C4EBB5E2978175127BBD4EDB8150D" xlink:to="loc_us-gaap_Revenues_47F8029DCC7401FF3B05BBD4EDB8C71B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_61E75679C1347034A8C9BBD4EDB8E931" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_8A1C4EBB5E2978175127BBD4EDB8150D" xlink:to="loc_us-gaap_CostsAndExpenses_61E75679C1347034A8C9BBD4EDB8E931" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="loc_us-gaap_DepreciationAndAmortization_48E4D28A27C9ACD52E18BBD4EDB87A09" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_8A1C4EBB5E2978175127BBD4EDB8150D" xlink:to="loc_us-gaap_DepreciationAndAmortization_48E4D28A27C9ACD52E18BBD4EDB87A09" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectOfChangesInRevenueRecognitionStatementOfIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_ECFB9E02F47D3E3208A4D4FB0F2F1F0D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_ECFB9E02F47D3E3208A4D4FB0F2F1F0D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_F5BB9B4CD8A0D49FE5E0D4FB0F2FB717" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_ECFB9E02F47D3E3208A4D4FB0F2F1F0D" xlink:to="loc_us-gaap_StatementScenarioAxis_F5BB9B4CD8A0D49FE5E0D4FB0F2FB717" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_F5BB9B4CD8A0D49FE5E0D4FB0F2FB717" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_F5BB9B4CD8A0D49FE5E0D4FB0F2FB717" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioPreviouslyReportedMember" xlink:label="loc_us-gaap_ScenarioPreviouslyReportedMember_3A519D9D934440AD1C72D4FB0F2F0FB8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF" xlink:to="loc_us-gaap_ScenarioPreviouslyReportedMember_3A519D9D934440AD1C72D4FB0F2F0FB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestatementAdjustmentMember" xlink:label="loc_us-gaap_RestatementAdjustmentMember_E1962383FAD5AA2C70BCD4FB0F2F9A02" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_1CE02BA0A9C39345DCA0D4FB0F2F70CF" xlink:to="loc_us-gaap_RestatementAdjustmentMember_E1962383FAD5AA2C70BCD4FB0F2F9A02" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_BC1777CADAB3C505A03CD4FB0F30535B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_ECFB9E02F47D3E3208A4D4FB0F2F1F0D" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_BC1777CADAB3C505A03CD4FB0F30535B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_11A39FB41CBC8CDC3A04D4FB0F3077AD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_BC1777CADAB3C505A03CD4FB0F30535B" xlink:to="loc_us-gaap_TypeOfAdoptionMember_11A39FB41CBC8CDC3A04D4FB0F3077AD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_11A39FB41CBC8CDC3A04D4FB0F3077AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_BC1777CADAB3C505A03CD4FB0F30535B" xlink:to="loc_us-gaap_TypeOfAdoptionMember_11A39FB41CBC8CDC3A04D4FB0F3077AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_FA705D45F6B58DE65327D4FB0F302E87" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_11A39FB41CBC8CDC3A04D4FB0F3077AD" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_FA705D45F6B58DE65327D4FB0F302E87" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_86A7A8B4350B62C5FD6DD4FB0F307B26" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_ECFB9E02F47D3E3208A4D4FB0F2F1F0D" xlink:to="loc_dei_LegalEntityAxis_86A7A8B4350B62C5FD6DD4FB0F307B26" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_63BCA96A9C0C5D8FBB7ED4FB0F30DF47_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_86A7A8B4350B62C5FD6DD4FB0F307B26" xlink:to="loc_dei_EntityDomain_63BCA96A9C0C5D8FBB7ED4FB0F30DF47_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_63BCA96A9C0C5D8FBB7ED4FB0F30DF47" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_86A7A8B4350B62C5FD6DD4FB0F307B26" xlink:to="loc_dei_EntityDomain_63BCA96A9C0C5D8FBB7ED4FB0F30DF47" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_0A3E63F8AA609E0A7DCFD4FB0F30B11A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_63BCA96A9C0C5D8FBB7ED4FB0F30DF47" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_0A3E63F8AA609E0A7DCFD4FB0F30B11A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_5FF2BDB1D0E72053E300D4FB0F30C0F2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:to="loc_us-gaap_Revenues_5FF2BDB1D0E72053E300D4FB0F30C0F2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_06BBE5CFC16F9FA1CC09D4FB0F30D129" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:to="loc_us-gaap_CostsAndExpenses_06BBE5CFC16F9FA1CC09D4FB0F30D129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_D5F12130F88AB917EB8CD4FB0F305801" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:to="loc_us-gaap_OperatingIncomeLoss_D5F12130F88AB917EB8CD4FB0F305801" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_AA457562D9BB76BC6AF5D4FB0F30A2FA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_DB1B97CD89D3BB21427DD4FB0F30DBFB" xlink:to="loc_us-gaap_NetIncomeLoss_AA457562D9BB76BC6AF5D4FB0F30A2FA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformEffectsOfChangesInRevenueRecognitionBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_EAC62053B941AEBD5B42FDD734CA24FD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_EAC62053B941AEBD5B42FDD734CA24FD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_20208707600728902A17FDD734CB9A8A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_EAC62053B941AEBD5B42FDD734CA24FD" xlink:to="loc_us-gaap_StatementScenarioAxis_20208707600728902A17FDD734CB9A8A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_20208707600728902A17FDD734CB9A8A" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_20208707600728902A17FDD734CB9A8A" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioPreviouslyReportedMember" xlink:label="loc_us-gaap_ScenarioPreviouslyReportedMember_05E8A56ED5EFA2D3F8E2FDD734CB66CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681" xlink:to="loc_us-gaap_ScenarioPreviouslyReportedMember_05E8A56ED5EFA2D3F8E2FDD734CB66CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestatementAdjustmentMember" xlink:label="loc_us-gaap_RestatementAdjustmentMember_BA2D167859288D4ED78FFDD734CCB6C2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_3D57D9C4FD8F14FE7C60FDD734CBB681" xlink:to="loc_us-gaap_RestatementAdjustmentMember_BA2D167859288D4ED78FFDD734CCB6C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_45643E7777217FB3B35EFDD734CA86FA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_EAC62053B941AEBD5B42FDD734CA24FD" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_45643E7777217FB3B35EFDD734CA86FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_B00021CA5E712C48083DFDD734CA0278_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_45643E7777217FB3B35EFDD734CA86FA" xlink:to="loc_us-gaap_TypeOfAdoptionMember_B00021CA5E712C48083DFDD734CA0278_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_B00021CA5E712C48083DFDD734CA0278" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_45643E7777217FB3B35EFDD734CA86FA" xlink:to="loc_us-gaap_TypeOfAdoptionMember_B00021CA5E712C48083DFDD734CA0278" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_1556F9CDC980103E89CBFDD734CAC349" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_B00021CA5E712C48083DFDD734CA0278" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_1556F9CDC980103E89CBFDD734CAC349" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_001DE55661481D45D147FDD734CB03CF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_EAC62053B941AEBD5B42FDD734CA24FD" xlink:to="loc_dei_LegalEntityAxis_001DE55661481D45D147FDD734CB03CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_AD11F7C5E40A24443950FDD734CB5F6B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_001DE55661481D45D147FDD734CB03CF" xlink:to="loc_dei_EntityDomain_AD11F7C5E40A24443950FDD734CB5F6B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_AD11F7C5E40A24443950FDD734CB5F6B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_001DE55661481D45D147FDD734CB03CF" xlink:to="loc_dei_EntityDomain_AD11F7C5E40A24443950FDD734CB5F6B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_D9A44437FB634FB0F35EFDD734CB8912" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_AD11F7C5E40A24443950FDD734CB5F6B" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_D9A44437FB634FB0F35EFDD734CB8912" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_0B9164F8BF2A2315F629FDD734CCB5D2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_AssetsCurrent_0B9164F8BF2A2315F629FDD734CCB5D2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmAndTelevisionCosts" xlink:label="loc_cmcsa_FilmAndTelevisionCosts_A577F3EBAF7D161BF54DFDD734CC42D0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_cmcsa_FilmAndTelevisionCosts_A577F3EBAF7D161BF54DFDD734CC42D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="loc_us-gaap_OtherIntangibleAssetsNet_004148ADCAEE87D59BCAFDD734CC5F54" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_OtherIntangibleAssetsNet_004148ADCAEE87D59BCAFDD734CC5F54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_C47DFDBF8E8B02EC8662FDD734CC7F91" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_C47DFDBF8E8B02EC8662FDD734CC7F91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_3E0CDCD7B0F45BD84503FDD734CCE967" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_Assets_3E0CDCD7B0F45BD84503FDD734CCE967" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_7B18B80C0F88A559AD55FDD734CDE206" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_LiabilitiesCurrent_7B18B80C0F88A559AD55FDD734CDE206" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_1596BEE4FE1056AD5A58FDD734CD76E0" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_1596BEE4FE1056AD5A58FDD734CD76E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_D51BDA42F97804924246FDD734CD57AF" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_D51BDA42F97804924246FDD734CD57AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_8C8D25DDFCEB895FB2D4FDD734CDD3C6" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_8C8D25DDFCEB895FB2D4FDD734CDD3C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_C922851BD6A932489335FDD734CD56E5" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_C922851BD6A932489335FDD734CD56E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_3C4252FAC04762BEF444FDD734CD519E" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F4041266EBB0CB4E001FDD734CC4952" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_3C4252FAC04762BEF444FDD734CD519E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F7E2C782798E27AECC5E38BAE4B138A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F7E2C782798E27AECC5E38BAE4B138A" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01983737FC205EACCADBE38BAE4A1454" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01983737FC205EACCADBE38BAE4A1454" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01983737FC205EACCADBE38BAE4A1454" xlink:to="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01983737FC205EACCADBE38BAE4A1454" xlink:to="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_MembersCapitalMember" xlink:label="loc_cmcsa_MembersCapitalMember_8717246FDAE4398BDC19E38BAE4AB726" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50" xlink:to="loc_cmcsa_MembersCapitalMember_8717246FDAE4398BDC19E38BAE4AB726" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_389E027612C6D081384BE38BAE4B6F5D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_61AA9EF81E2CD5660934E38BAE4A3C50" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_389E027612C6D081384BE38BAE4B6F5D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_E5B0B295975C3B968419E38BAE4B6DB7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_E5B0B295975C3B968419E38BAE4B6DB7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_E77EE1BF66329A152E9FE38BAE4B3BB0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_E5B0B295975C3B968419E38BAE4B6DB7" xlink:to="loc_us-gaap_TypeOfAdoptionMember_E77EE1BF66329A152E9FE38BAE4B3BB0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_E77EE1BF66329A152E9FE38BAE4B3BB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_E5B0B295975C3B968419E38BAE4B6DB7" xlink:to="loc_us-gaap_TypeOfAdoptionMember_E77EE1BF66329A152E9FE38BAE4B3BB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201601Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201601Member_8EF692ACF318FDD432F1E38BAE4B9127" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_E77EE1BF66329A152E9FE38BAE4B3BB0" xlink:to="loc_us-gaap_AccountingStandardsUpdate201601Member_8EF692ACF318FDD432F1E38BAE4B9127" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_A573453442119B4EDE7BE38BAE4B0011" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:to="loc_us-gaap_StatementScenarioAxis_A573453442119B4EDE7BE38BAE4B0011" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_A573453442119B4EDE7BE38BAE4B0011" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_A573453442119B4EDE7BE38BAE4B0011" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScenarioPreviouslyReportedMember" xlink:label="loc_us-gaap_ScenarioPreviouslyReportedMember_32AF5FDEA7CB6EA3AFC3E38BAE4BC536" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38" xlink:to="loc_us-gaap_ScenarioPreviouslyReportedMember_32AF5FDEA7CB6EA3AFC3E38BAE4BC536" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestatementAdjustmentMember" xlink:label="loc_us-gaap_RestatementAdjustmentMember_BAD79B116E40D7D0E678E38BAE4BED2E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_AC475B75959DE6524891E38BAE4B2D38" xlink:to="loc_us-gaap_RestatementAdjustmentMember_BAD79B116E40D7D0E678E38BAE4BED2E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_BE80CA87CAA9BBE980A1E38BAE4BCAEF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_AE4E6A5A8852DD7C621FE38BAE4A654F" xlink:to="loc_dei_LegalEntityAxis_BE80CA87CAA9BBE980A1E38BAE4BCAEF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_91D53020DF3AA9A16B9CE38BAE4BC146_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_BE80CA87CAA9BBE980A1E38BAE4BCAEF" xlink:to="loc_dei_EntityDomain_91D53020DF3AA9A16B9CE38BAE4BC146_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_91D53020DF3AA9A16B9CE38BAE4BC146" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_BE80CA87CAA9BBE980A1E38BAE4BCAEF" xlink:to="loc_dei_EntityDomain_91D53020DF3AA9A16B9CE38BAE4BC146" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_7D092EEF66A01FF60367E38BAE4B31E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91D53020DF3AA9A16B9CE38BAE4BC146" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_7D092EEF66A01FF60367E38BAE4B31E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_E023FA0BB0447A44A467E38BAE4CB703" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F7E2C782798E27AECC5E38BAE4B138A" xlink:to="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_E023FA0BB0447A44A467E38BAE4CB703" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_IncomeTaxBenefit2017TaxReformLegislation" xlink:label="loc_cmcsa_IncomeTaxBenefit2017TaxReformLegislation_2D122F2CD67D3F5D1AB3E38BAE4C6DD4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F7E2C782798E27AECC5E38BAE4B138A" xlink:to="loc_cmcsa_IncomeTaxBenefit2017TaxReformLegislation_2D122F2CD67D3F5D1AB3E38BAE4C6DD4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_IncomeTaxBenefit2018TaxReformLegislation" xlink:label="loc_cmcsa_IncomeTaxBenefit2018TaxReformLegislation_02478CAF1D04DA178CABE38BAE4CDEC1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_7F7E2C782798E27AECC5E38BAE4B138A" xlink:to="loc_cmcsa_IncomeTaxBenefit2018TaxReformLegislation_02478CAF1D04DA178CABE38BAE4CDEC1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsAndTaxReformTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1BD07048AB2DC4C0F1DAFDD701C257AE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_FB5EF60B8DEAE654315CFDD701C21AE3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1BD07048AB2DC4C0F1DAFDD701C257AE" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_FB5EF60B8DEAE654315CFDD701C21AE3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_5DE210D3091261DB625CFDD701C28658" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_FB5EF60B8DEAE654315CFDD701C21AE3" xlink:to="loc_dei_LegalEntityAxis_5DE210D3091261DB625CFDD701C28658" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_8C9B8B273D3CFAFB17E0FDD701C25797_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5DE210D3091261DB625CFDD701C28658" xlink:to="loc_dei_EntityDomain_8C9B8B273D3CFAFB17E0FDD701C25797_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_8C9B8B273D3CFAFB17E0FDD701C25797" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5DE210D3091261DB625CFDD701C28658" xlink:to="loc_dei_EntityDomain_8C9B8B273D3CFAFB17E0FDD701C25797" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_0D0D9AB83F58A47D16D7FDD701C21B24" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8C9B8B273D3CFAFB17E0FDD701C25797" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_0D0D9AB83F58A47D16D7FDD701C21B24" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:label="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_5BCF2EE679683CBCBDD0FDD701C317EF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_1BD07048AB2DC4C0F1DAFDD701C257AE" xlink:to="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_5BCF2EE679683CBCBDD0FDD701C317EF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RelatedPartyTransactions" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_179892AC0657245C4FA7FC1E36FAE10A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_DC6485B3A6D3928AA747FC1E36FA0E4F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_179892AC0657245C4FA7FC1E36FAE10A" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_DC6485B3A6D3928AA747FC1E36FA0E4F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_96A4A7D191B93D912000FC1E36FAF58F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_DC6485B3A6D3928AA747FC1E36FA0E4F" xlink:to="loc_dei_LegalEntityAxis_96A4A7D191B93D912000FC1E36FAF58F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FD545F0A343EADB4E215FC1E36FA2A61_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_96A4A7D191B93D912000FC1E36FAF58F" xlink:to="loc_dei_EntityDomain_FD545F0A343EADB4E215FC1E36FA2A61_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FD545F0A343EADB4E215FC1E36FA2A61" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_96A4A7D191B93D912000FC1E36FAF58F" xlink:to="loc_dei_EntityDomain_FD545F0A343EADB4E215FC1E36FA2A61" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_EA1CD41FF27FF0A21D9FFC1E36FA30EE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FD545F0A343EADB4E215FC1E36FA2A61" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_EA1CD41FF27FF0A21D9FFC1E36FA30EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionsDisclosureTextBlock" xlink:label="loc_us-gaap_RelatedPartyTransactionsDisclosureTextBlock_B1E5053781CE6602BEBFFC1E36FA7163" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_179892AC0657245C4FA7FC1E36FAE10A" xlink:to="loc_us-gaap_RelatedPartyTransactionsDisclosureTextBlock_B1E5053781CE6602BEBFFC1E36FA7163" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RelatedPartyTransactionsCondensedConsolidatedBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_92DD7CBD162CFF89836C9294235C4A05" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_92DD7CBD162CFF89836C9294235C4A05" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_8B9740C4D3F52969E313929423617A89" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_92DD7CBD162CFF89836C9294235C4A05" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_8B9740C4D3F52969E313929423617A89" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_2A903C01724E738FCFDE9294236182DC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_8B9740C4D3F52969E313929423617A89" xlink:to="loc_us-gaap_RelatedPartyDomain_2A903C01724E738FCFDE9294236182DC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_2A903C01724E738FCFDE9294236182DC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_8B9740C4D3F52969E313929423617A89" xlink:to="loc_us-gaap_RelatedPartyDomain_2A903C01724E738FCFDE9294236182DC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastAndConsolidatedSubsidiariesMember" xlink:label="loc_cmcsa_ComcastAndConsolidatedSubsidiariesMember_D1DB0B1E20289411BFF092942361200A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_2A903C01724E738FCFDE9294236182DC" xlink:to="loc_cmcsa_ComcastAndConsolidatedSubsidiariesMember_D1DB0B1E20289411BFF092942361200A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_0D6DE3497EA2E489B60E92942361BB6F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_92DD7CBD162CFF89836C9294235C4A05" xlink:to="loc_dei_LegalEntityAxis_0D6DE3497EA2E489B60E92942361BB6F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_52A621AE214B8AE6C13C9294236299E9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0D6DE3497EA2E489B60E92942361BB6F" xlink:to="loc_dei_EntityDomain_52A621AE214B8AE6C13C9294236299E9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_52A621AE214B8AE6C13C9294236299E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0D6DE3497EA2E489B60E92942361BB6F" xlink:to="loc_dei_EntityDomain_52A621AE214B8AE6C13C9294236299E9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_C3AD0C8934D58B75163192942362B463" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_52A621AE214B8AE6C13C9294236299E9" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_C3AD0C8934D58B75163192942362B463" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_5BA568746CCEF13126E992942362B0B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_5BA568746CCEF13126E992942362B0B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_116098D8BB09C3F186D292942362A938" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_AccountsPayableCurrent_116098D8BB09C3F186D292942362A938" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_A8D5A3FDC8AA719F1F549294236201B6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_A8D5A3FDC8AA719F1F549294236201B6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NotePayableToUltimateParent" xlink:label="loc_cmcsa_NotePayableToUltimateParent_2839D7BCBBCC176342039294236231D2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_cmcsa_NotePayableToUltimateParent_2839D7BCBBCC176342039294236231D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_1A2C4AAC4E16A23DFB309294236270B3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_1A2C4AAC4E16A23DFB309294236270B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_E33B8B8008246DF665FF929423621680" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_1FD4C4057CE1B26BB377929423622CF9" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_E33B8B8008246DF665FF929423621680" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RelatedPartyTransactionsCondensedConsolidatedStatementOfIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_C174C26B34D7F943A75AE3C041341642" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F1AAD2C40B1DE3569BD7E3C0413492D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_C174C26B34D7F943A75AE3C041341642" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F1AAD2C40B1DE3569BD7E3C0413492D0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_B984183C3E96833B583AE3C04134EE32" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F1AAD2C40B1DE3569BD7E3C0413492D0" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_B984183C3E96833B583AE3C04134EE32" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_E7A459CCE07F5F03A338E3C041348A63_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_B984183C3E96833B583AE3C04134EE32" xlink:to="loc_us-gaap_RelatedPartyDomain_E7A459CCE07F5F03A338E3C041348A63_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_E7A459CCE07F5F03A338E3C041348A63" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_B984183C3E96833B583AE3C04134EE32" xlink:to="loc_us-gaap_RelatedPartyDomain_E7A459CCE07F5F03A338E3C041348A63" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ComcastAndConsolidatedSubsidiariesMember" xlink:label="loc_cmcsa_ComcastAndConsolidatedSubsidiariesMember_B87507DCD588B1D3B79DE3C0413442CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_E7A459CCE07F5F03A338E3C041348A63" xlink:to="loc_cmcsa_ComcastAndConsolidatedSubsidiariesMember_B87507DCD588B1D3B79DE3C0413442CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_610C8A2D1788CF4BA3B5E3C041347039" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F1AAD2C40B1DE3569BD7E3C0413492D0" xlink:to="loc_dei_LegalEntityAxis_610C8A2D1788CF4BA3B5E3C041347039" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_29947F0D960A5664B9BFE3C04134F5EF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_610C8A2D1788CF4BA3B5E3C041347039" xlink:to="loc_dei_EntityDomain_29947F0D960A5664B9BFE3C04134F5EF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_29947F0D960A5664B9BFE3C04134F5EF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_610C8A2D1788CF4BA3B5E3C041347039" xlink:to="loc_dei_EntityDomain_29947F0D960A5664B9BFE3C04134F5EF" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_B0E6399B8236C37E9D2EE3C04134512E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_29947F0D960A5664B9BFE3C04134F5EF" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_B0E6399B8236C37E9D2EE3C04134512E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_066784335A8C6CF87924E3C0413492E8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_C174C26B34D7F943A75AE3C041341642" xlink:to="loc_us-gaap_Revenues_066784335A8C6CF87924E3C0413492E8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaap_CostsAndExpenses_D8DFBEDA9F4626F0A487E3C041341732" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_C174C26B34D7F943A75AE3C041341642" xlink:to="loc_us-gaap_CostsAndExpenses_D8DFBEDA9F4626F0A487E3C041341732" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherIncomeExpenseRelatedParty" xlink:label="loc_cmcsa_OtherIncomeExpenseRelatedParty_B08A542F16B22890C7E3E3C041341260" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_C174C26B34D7F943A75AE3C041341642" xlink:to="loc_cmcsa_OtherIncomeExpenseRelatedParty_B08A542F16B22890C7E3E3C041341260" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_D27C6D0052C975017BFDFC7B7A3F67F8" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F278E77FD448D43FF6A3FC7B7A3EA895" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_D27C6D0052C975017BFDFC7B7A3F67F8" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F278E77FD448D43FF6A3FC7B7A3EA895" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_CBC3ECABF36E925E047AFC7B7A3F6182" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F278E77FD448D43FF6A3FC7B7A3EA895" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_CBC3ECABF36E925E047AFC7B7A3F6182" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_247ECAACA230D0FE48DBFC7B7A3F2209_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_CBC3ECABF36E925E047AFC7B7A3F6182" xlink:to="loc_us-gaap_RelatedPartyDomain_247ECAACA230D0FE48DBFC7B7A3F2209_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_247ECAACA230D0FE48DBFC7B7A3F2209" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_CBC3ECABF36E925E047AFC7B7A3F6182" xlink:to="loc_us-gaap_RelatedPartyDomain_247ECAACA230D0FE48DBFC7B7A3F2209" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CarryingValueOfRelatedPartyContractualObligationMember" xlink:label="loc_cmcsa_CarryingValueOfRelatedPartyContractualObligationMember_5CEE177D9288B062B862FC7B7A3F163A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_247ECAACA230D0FE48DBFC7B7A3F2209" xlink:to="loc_cmcsa_CarryingValueOfRelatedPartyContractualObligationMember_5CEE177D9288B062B862FC7B7A3F163A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_2355C33E6B3CFF1507DEFC7B7A3F937F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_F278E77FD448D43FF6A3FC7B7A3EA895" xlink:to="loc_dei_LegalEntityAxis_2355C33E6B3CFF1507DEFC7B7A3F937F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5E7FF6CB3B61EA09235BFC7B7A3F9A19_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_2355C33E6B3CFF1507DEFC7B7A3F937F" xlink:to="loc_dei_EntityDomain_5E7FF6CB3B61EA09235BFC7B7A3F9A19_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5E7FF6CB3B61EA09235BFC7B7A3F9A19" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_2355C33E6B3CFF1507DEFC7B7A3F937F" xlink:to="loc_dei_EntityDomain_5E7FF6CB3B61EA09235BFC7B7A3F9A19" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_CB279087552D66361356FC7B7A3FED99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5E7FF6CB3B61EA09235BFC7B7A3F9A19" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_CB279087552D66361356FC7B7A3FED99" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_85E3352626F3DB3DBDA8FC7B7A3F477A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_D27C6D0052C975017BFDFC7B7A3F67F8" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_85E3352626F3DB3DBDA8FC7B7A3F477A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_A555539812CDD18E34B5FC8299E14A4F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_D27C6D0052C975017BFDFC7B7A3F67F8" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_A555539812CDD18E34B5FC8299E14A4F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RelatedPartyTransactionsTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_8EC55B6FA976ADF06838FC1E36F87A60" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5AD0DDA21D8C240A509EFC1E36F71B9C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8EC55B6FA976ADF06838FC1E36F87A60" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5AD0DDA21D8C240A509EFC1E36F71B9C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_C34630BC252897940BBCFC1E36F7AF43" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_5AD0DDA21D8C240A509EFC1E36F71B9C" xlink:to="loc_dei_LegalEntityAxis_C34630BC252897940BBCFC1E36F7AF43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D3CBF505B5C2E49ECFFFC1E36F81CE1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_C34630BC252897940BBCFC1E36F7AF43" xlink:to="loc_dei_EntityDomain_3D3CBF505B5C2E49ECFFFC1E36F81CE1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D3CBF505B5C2E49ECFFFC1E36F81CE1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_C34630BC252897940BBCFC1E36F7AF43" xlink:to="loc_dei_EntityDomain_3D3CBF505B5C2E49ECFFFC1E36F81CE1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_E12D3EA3A3C0FC9ECD1DFC1E36F891F3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3CBF505B5C2E49ECFFFC1E36F81CE1" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_E12D3EA3A3C0FC9ECD1DFC1E36F891F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsTableTextBlock_6AE9B706E708542BE7B9FC1E36F8749B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8EC55B6FA976ADF06838FC1E36F87A60" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsTableTextBlock_6AE9B706E708542BE7B9FC1E36F8749B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/Revenue" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_EC623184635ED0A4B72EF3D8474A3DB6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_8F474CAD068E05CE7634F3D8474A5CB3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_EC623184635ED0A4B72EF3D8474A3DB6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_8F474CAD068E05CE7634F3D8474A5CB3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_EE186B7963E3904E3E99F3D8474A6ED8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_8F474CAD068E05CE7634F3D8474A5CB3" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_EE186B7963E3904E3E99F3D8474A6ED8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_59CF06A4F469F43511D1F3D8474ACAEB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_EE186B7963E3904E3E99F3D8474A6ED8" xlink:to="loc_us-gaap_TypeOfAdoptionMember_59CF06A4F469F43511D1F3D8474ACAEB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_59CF06A4F469F43511D1F3D8474ACAEB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_EE186B7963E3904E3E99F3D8474A6ED8" xlink:to="loc_us-gaap_TypeOfAdoptionMember_59CF06A4F469F43511D1F3D8474ACAEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_576C7CE9BD52A3300898F3D8474A45CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_59CF06A4F469F43511D1F3D8474ACAEB" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_576C7CE9BD52A3300898F3D8474A45CD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_E140D886EEC8FBA7F368F3D8474A1848" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_8F474CAD068E05CE7634F3D8474A5CB3" xlink:to="loc_dei_LegalEntityAxis_E140D886EEC8FBA7F368F3D8474A1848" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_419DD4190D1E648BAF70F3D8474AD5FB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_E140D886EEC8FBA7F368F3D8474A1848" xlink:to="loc_dei_EntityDomain_419DD4190D1E648BAF70F3D8474AD5FB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_419DD4190D1E648BAF70F3D8474AD5FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_E140D886EEC8FBA7F368F3D8474A1848" xlink:to="loc_dei_EntityDomain_419DD4190D1E648BAF70F3D8474AD5FB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_66871E3E1A45DBB2FED0F3D8474A7CA2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_419DD4190D1E648BAF70F3D8474AD5FB" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_66871E3E1A45DBB2FED0F3D8474A7CA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_9CEA77229AE5D9FAA5F8F3D8474AF009" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_EC623184635ED0A4B72EF3D8474A3DB6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_9CEA77229AE5D9FAA5F8F3D8474AF009" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueCondensedConsolidatedBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_167510BC3D0E66C7E4C3E38045D9BF64" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_167510BC3D0E66C7E4C3E38045D9BF64" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_4552944631AE96F060A1E38045DA7DBE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_167510BC3D0E66C7E4C3E38045D9BF64" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_4552944631AE96F060A1E38045DA7DBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_B811F22F26F3D18152A8E38045DAF989_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_4552944631AE96F060A1E38045DA7DBE" xlink:to="loc_us-gaap_TypeOfAdoptionMember_B811F22F26F3D18152A8E38045DAF989_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_B811F22F26F3D18152A8E38045DAF989" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_4552944631AE96F060A1E38045DA7DBE" xlink:to="loc_us-gaap_TypeOfAdoptionMember_B811F22F26F3D18152A8E38045DAF989" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_32F325400F1895648312E38045DA5B09" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_B811F22F26F3D18152A8E38045DAF989" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_32F325400F1895648312E38045DA5B09" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_439AC63536F705ACA8EAE38045DB9E7E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_167510BC3D0E66C7E4C3E38045D9BF64" xlink:to="loc_dei_LegalEntityAxis_439AC63536F705ACA8EAE38045DB9E7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C105AA0784DDC9C80F75E38045DBAC5E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_439AC63536F705ACA8EAE38045DB9E7E" xlink:to="loc_dei_EntityDomain_C105AA0784DDC9C80F75E38045DBAC5E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C105AA0784DDC9C80F75E38045DBAC5E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_439AC63536F705ACA8EAE38045DB9E7E" xlink:to="loc_dei_EntityDomain_C105AA0784DDC9C80F75E38045DBAC5E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_835A1830C9FA817193D8E38045DB1CE1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C105AA0784DDC9C80F75E38045DBAC5E" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_835A1830C9FA817193D8E38045DB1CE1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableGrossCurrent" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_C8F80B7365A3A0AA1625E38045DC196A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_C8F80B7365A3A0AA1625E38045DC196A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_775C0DC25118F80CA2F0E38045DC371D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_775C0DC25118F80CA2F0E38045DC371D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_13D207319DB02010E905E38045DCC042" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_13D207319DB02010E905E38045DCC042" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetNoncurrent" xlink:label="loc_us-gaap_AccountsReceivableNetNoncurrent_25F92BA003376EA1EAF9E38045E1CDD0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_AccountsReceivableNetNoncurrent_25F92BA003376EA1EAF9E38045E1CDD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostNet" xlink:label="loc_us-gaap_CapitalizedContractCostNet_4C1FF3C36CAD1680FC31E38045E23C60" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_CapitalizedContractCostNet_4C1FF3C36CAD1680FC31E38045E23C60" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredRevenueNoncurrent" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_1DE74A7D97F1A2D20A61E38045E2D603" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_920EC3C566EC6C664791E38045DCB9A8" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_1DE74A7D97F1A2D20A61E38045E2D603" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_DB0E35BDACE809AAA7F5FDD735FE84D3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_DB0E35BDACE809AAA7F5FDD735FE84D3" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_3CF5D0FBD0DD5A791CD1FDD735F9A8F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:to="loc_dei_LegalEntityAxis_3CF5D0FBD0DD5A791CD1FDD735F9A8F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FF990B859C2A20F6B98EFDD735FA89E5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_3CF5D0FBD0DD5A791CD1FDD735F9A8F4" xlink:to="loc_dei_EntityDomain_FF990B859C2A20F6B98EFDD735FA89E5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FF990B859C2A20F6B98EFDD735FA89E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_3CF5D0FBD0DD5A791CD1FDD735F9A8F4" xlink:to="loc_dei_EntityDomain_FF990B859C2A20F6B98EFDD735FA89E5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_B2D4C814BC40FF2745FBFDD735FA21BE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FF990B859C2A20F6B98EFDD735FA89E5" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_B2D4C814BC40FF2745FBFDD735FA21BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_6668D65F3CEA8C3FC69BFDD735FA2713" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:to="loc_us-gaap_ConsolidationItemsAxis_6668D65F3CEA8C3FC69BFDD735FA2713" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_6668D65F3CEA8C3FC69BFDD735FA2713" xlink:to="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_6668D65F3CEA8C3FC69BFDD735FA2713" xlink:to="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="loc_us-gaap_CorporateNonSegmentMember_D40461F89B2A684B0E57FDD735FA6C9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20" xlink:to="loc_us-gaap_CorporateNonSegmentMember_D40461F89B2A684B0E57FDD735FA6C9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaterialReconcilingItemsMember" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_3B3EB5088217CD2F30B0FDD735FB7B2F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_AE9A5E4DC3DBD810B3BFFDD735FA3B20" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_3B3EB5088217CD2F30B0FDD735FB7B2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_5CFF5A0989F3818A7979FDD735FBBBBB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_5CFF5A0989F3818A7979FDD735FBBBBB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5CFF5A0989F3818A7979FDD735FBBBBB" xlink:to="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5CFF5A0989F3818A7979FDD735FBBBBB" xlink:to="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_560ECB230732A3767F3EFDD735FB43D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_CableCommunicationsMember_560ECB230732A3767F3EFDD735FB43D9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableNetworksMember" xlink:label="loc_cmcsa_CableNetworksMember_AFC2C92A33889475673CFDD735FBCD1E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_CableNetworksMember_AFC2C92A33889475673CFDD735FBCD1E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BroadcastTelevisionMember" xlink:label="loc_cmcsa_BroadcastTelevisionMember_DEBE96A3E7C66DCFAE9BFDD735FBA3E0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_BroadcastTelevisionMember_DEBE96A3E7C66DCFAE9BFDD735FBA3E0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmedEntertainmentMember" xlink:label="loc_cmcsa_FilmedEntertainmentMember_02347AB6E5BD533A1DDAFDD735FBF382" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_FilmedEntertainmentMember_02347AB6E5BD533A1DDAFDD735FBF382" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ThemeParksMember" xlink:label="loc_cmcsa_ThemeParksMember_5550436490C8CACE9B18FDD735FC883A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_ThemeParksMember_5550436490C8CACE9B18FDD735FC883A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalSegmentsMember" xlink:label="loc_cmcsa_NBCUniversalSegmentsMember_4375A80A64A9AEEDC157FDD735FCDA4D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2DA8FF549FC186E356DAFDD735FB4881" xlink:to="loc_cmcsa_NBCUniversalSegmentsMember_4375A80A64A9AEEDC157FDD735FCDA4D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_BA5F9153F6DA0D40CA43FDD735FCFE3E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_3EC7F69C1DCF2AFB323AFDD735F9CCB7" xlink:to="loc_us-gaap_ProductOrServiceAxis_BA5F9153F6DA0D40CA43FDD735FCFE3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_BA5F9153F6DA0D40CA43FDD735FCFE3E" xlink:to="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_BA5F9153F6DA0D40CA43FDD735FCFE3E" xlink:to="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialVideoMember" xlink:label="loc_cmcsa_ResidentialVideoMember_6054EA0FA17EB1DCC65DFDD735FC9461" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_ResidentialVideoMember_6054EA0FA17EB1DCC65DFDD735FC9461" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialHighSpeedInternetMember" xlink:label="loc_cmcsa_ResidentialHighSpeedInternetMember_709E2C51BF58AF3A83C0FDD735FC050B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_ResidentialHighSpeedInternetMember_709E2C51BF58AF3A83C0FDD735FC050B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialVoiceMember" xlink:label="loc_cmcsa_ResidentialVoiceMember_0D396321BD5090A729F9FDD735FD9A3E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_ResidentialVoiceMember_0D396321BD5090A729F9FDD735FD9A3E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessServicesMember" xlink:label="loc_cmcsa_BusinessServicesMember_1C831B18BA17BE915DC6FDD735FD1090" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_BusinessServicesMember_1C831B18BA17BE915DC6FDD735FD1090" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DistributionMember" xlink:label="loc_cmcsa_DistributionMember_A3D17EC70D872ADEF3EDFDD735FD8B01" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_DistributionMember_A3D17EC70D872ADEF3EDFDD735FD8B01" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AdvertisingMember" xlink:label="loc_cmcsa_AdvertisingMember_D0D9B7B930E79CB51FBDFDD735FD5D05" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_AdvertisingMember_D0D9B7B930E79CB51FBDFDD735FD5D05" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ContentLicensingAndOtherMember" xlink:label="loc_cmcsa_ContentLicensingAndOtherMember_F3F64B0F4C13FF5C0EB5FDD735FD9D88" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_ContentLicensingAndOtherMember_F3F64B0F4C13FF5C0EB5FDD735FD9D88" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_TheatricalMember" xlink:label="loc_cmcsa_TheatricalMember_9A545705F6355CD560DEFDD735FDC908" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_TheatricalMember_9A545705F6355CD560DEFDD735FDC908" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ContentLicensingMember" xlink:label="loc_cmcsa_ContentLicensingMember_719C48FD8CE8BC47C675FDD735FEE300" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_ContentLicensingMember_719C48FD8CE8BC47C675FDD735FEE300" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DistributionAndOtherMember" xlink:label="loc_cmcsa_DistributionAndOtherMember_3725EF1E0430279387C9FDD735FE2473" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_DistributionAndOtherMember_3725EF1E0430279387C9FDD735FE2473" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_HomeEntertainmentMember" xlink:label="loc_cmcsa_HomeEntertainmentMember_864B23DC3AECCD0A687BFDD735FE6BE2" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_HomeEntertainmentMember_864B23DC3AECCD0A687BFDD735FE6BE2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_OtherMember" xlink:label="loc_cmcsa_OtherMember_773868B2C8784E3AE7AFFDD735FE55A8" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_OtherMember_773868B2C8784E3AE7AFFDD735FE55A8" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FranchiseAndOtherRegulatoryFeesMember" xlink:label="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_5DF954AF42D1A11CF9B6FDD735FCAF3A" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_6DB375E2282F6AF67B21FDD735FC92FE" xlink:to="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_5DF954AF42D1A11CF9B6FDD735FCAF3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_AA6961E0587E38EADE7BFDD735FE7F2B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_DB0E35BDACE809AAA7F5FDD735FE84D3" xlink:to="loc_us-gaap_Revenues_AA6961E0587E38EADE7BFDD735FE7F2B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue" xlink:label="loc_cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue_974346B0B486910B8F4CFDD735FF1E6D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_DB0E35BDACE809AAA7F5FDD735FE84D3" xlink:to="loc_cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue_974346B0B486910B8F4CFDD735FF1E6D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_9E4649C65B77ACA7892BF82269CD50F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:to="loc_dei_LegalEntityAxis_9E4649C65B77ACA7892BF82269CD50F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D1FF79D4B851D5B4989F82269CD1E06_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9E4649C65B77ACA7892BF82269CD50F9" xlink:to="loc_dei_EntityDomain_3D1FF79D4B851D5B4989F82269CD1E06_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D1FF79D4B851D5B4989F82269CD1E06" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9E4649C65B77ACA7892BF82269CD50F9" xlink:to="loc_dei_EntityDomain_3D1FF79D4B851D5B4989F82269CD1E06" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_89546341812C4285A5D0F82269CD9F4F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D1FF79D4B851D5B4989F82269CD1E06" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_89546341812C4285A5D0F82269CD9F4F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_C876111B2C9B5E8C5895F82269CDA5AD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:to="loc_us-gaap_ConsolidationItemsAxis_C876111B2C9B5E8C5895F82269CDA5AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_EBDB2B2E0EFA382B67D6F82269CD70F2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_C876111B2C9B5E8C5895F82269CDA5AD" xlink:to="loc_us-gaap_ConsolidationItemsDomain_EBDB2B2E0EFA382B67D6F82269CD70F2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_EBDB2B2E0EFA382B67D6F82269CD70F2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_C876111B2C9B5E8C5895F82269CDA5AD" xlink:to="loc_us-gaap_ConsolidationItemsDomain_EBDB2B2E0EFA382B67D6F82269CD70F2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingSegmentsMember" xlink:label="loc_us-gaap_OperatingSegmentsMember_76F335ABAAE084BE609DF82269CD59A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_EBDB2B2E0EFA382B67D6F82269CD70F2" xlink:to="loc_us-gaap_OperatingSegmentsMember_76F335ABAAE084BE609DF82269CD59A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_34D03241B3584B2CA330F82269CDE315" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_34D03241B3584B2CA330F82269CDE315" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_34D03241B3584B2CA330F82269CDE315" xlink:to="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_34D03241B3584B2CA330F82269CDE315" xlink:to="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_CDDB4C2F55D95FD31FE0F82269CDB7C3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:to="loc_cmcsa_CableCommunicationsMember_CDDB4C2F55D95FD31FE0F82269CDB7C3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableNetworksMember" xlink:label="loc_cmcsa_CableNetworksMember_7E7634CF3104895203E8F82269CD9B37" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:to="loc_cmcsa_CableNetworksMember_7E7634CF3104895203E8F82269CD9B37" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BroadcastTelevisionMember" xlink:label="loc_cmcsa_BroadcastTelevisionMember_0EEF6178E1FD40E41ABCF82269CDAA32" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:to="loc_cmcsa_BroadcastTelevisionMember_0EEF6178E1FD40E41ABCF82269CDAA32" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmedEntertainmentMember" xlink:label="loc_cmcsa_FilmedEntertainmentMember_19B44F9A083CC733D791F82269CD95D9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2D095BD8927F6918CC5BF82269CD07F4" xlink:to="loc_cmcsa_FilmedEntertainmentMember_19B44F9A083CC733D791F82269CD95D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_0C81C51F48BEDCDC2310F82269CD1555" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:to="loc_us-gaap_ProductOrServiceAxis_0C81C51F48BEDCDC2310F82269CD1555" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_0C81C51F48BEDCDC2310F82269CD1555" xlink:to="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_0C81C51F48BEDCDC2310F82269CD1555" xlink:to="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ResidentialMember" xlink:label="loc_cmcsa_ResidentialMember_22B54663FC2FBEA21E09F82269CDC868" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_ResidentialMember_22B54663FC2FBEA21E09F82269CDC868" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_DistributionMember" xlink:label="loc_cmcsa_DistributionMember_E27826CB2AA67E01AA45F82269CDEB73" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_DistributionMember_E27826CB2AA67E01AA45F82269CDEB73" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FranchiseAndOtherRegulatoryFeesMember" xlink:label="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_AF84C2951CF3960FDD88F82269CD27C3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_AF84C2951CF3960FDD88F82269CD27C3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessServicesMember" xlink:label="loc_cmcsa_BusinessServicesMember_7021FFF5E8B3D8A1F9EAF82269CD9B36" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_BusinessServicesMember_7021FFF5E8B3D8A1F9EAF82269CD9B36" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AdvertisingMember" xlink:label="loc_cmcsa_AdvertisingMember_4C1F36DE731A1D273083F82269CD5361" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_AdvertisingMember_4C1F36DE731A1D273083F82269CD5361" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_TheatricalMember" xlink:label="loc_cmcsa_TheatricalMember_29428A964498402C8579F82269CDEAB6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_TheatricalMember_29428A964498402C8579F82269CDEAB6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ContentLicensingMember" xlink:label="loc_cmcsa_ContentLicensingMember_A4AACB975F9EF4A36B81F82269CDAA85" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_ContentLicensingMember_A4AACB975F9EF4A36B81F82269CDAA85" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_HomeEntertainmentMember" xlink:label="loc_cmcsa_HomeEntertainmentMember_15264FA6257946D7A8B4F82269CDC0C3" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_3E8D318C8F289C02014BF82269CDA741" xlink:to="loc_cmcsa_HomeEntertainmentMember_15264FA6257946D7A8B4F82269CDC0C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_E354B33C1737CAB0CDADF82269CD4C2C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_BDE002546959853BBC06F82269CD8BB2" xlink:to="loc_us-gaap_RangeAxis_E354B33C1737CAB0CDADF82269CD4C2C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_E354B33C1737CAB0CDADF82269CD4C2C" xlink:to="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_E354B33C1737CAB0CDADF82269CD4C2C" xlink:to="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_7440CBF5FE24A7D8FE07F82269CD56DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421" xlink:to="loc_us-gaap_MinimumMember_7440CBF5FE24A7D8FE07F82269CD56DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_443737B30169997597CAF82269CD8179" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F7AA6CF350A8D6947DB5F82269CDA421" xlink:to="loc_us-gaap_MaximumMember_443737B30169997597CAF82269CD8179" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RevenuePerformanceObligationDescriptionOfTimingTermOfContract" xlink:label="loc_cmcsa_RevenuePerformanceObligationDescriptionOfTimingTermOfContract_EF43E70C474B0BA1446EF82269CDC40B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:to="loc_cmcsa_RevenuePerformanceObligationDescriptionOfTimingTermOfContract_EF43E70C474B0BA1446EF82269CDC40B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod_B104BA4FDE767503C971F82269CDBB19" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod_B104BA4FDE767503C971F82269CDBB19" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_RevenuePerformanceObligationDescriptionOfPaymentTermsPeriod" xlink:label="loc_cmcsa_RevenuePerformanceObligationDescriptionOfPaymentTermsPeriod_EDF8B7819C6950F580B0F82269CDDADD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:to="loc_cmcsa_RevenuePerformanceObligationDescriptionOfPaymentTermsPeriod_EDF8B7819C6950F580B0F82269CDDADD" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_Annualrevenuethatestimatesremainingperformanceobligations" xlink:label="loc_cmcsa_Annualrevenuethatestimatesremainingperformanceobligations_1FA6AD5C97A391F72CE5F82269CDCBBE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_E72DFD9A33C6E1A6A8B2F82269CDA04B" xlink:to="loc_cmcsa_Annualrevenuethatestimatesremainingperformanceobligations_1FA6AD5C97A391F72CE5F82269CDCBBE" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueRevenueByGeographicLocationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_1B245B7F9551DA52DE7DF822B89F7C71" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_182FA13BBA7E0CDBA220F822B89BB429" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1B245B7F9551DA52DE7DF822B89F7C71" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_182FA13BBA7E0CDBA220F822B89BB429" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_884AFAFADA9D707C27F1F822B89D662B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_182FA13BBA7E0CDBA220F822B89BB429" xlink:to="loc_dei_LegalEntityAxis_884AFAFADA9D707C27F1F822B89D662B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FAE8F5F8AF58DB8C7A93F822B89E5C21_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_884AFAFADA9D707C27F1F822B89D662B" xlink:to="loc_dei_EntityDomain_FAE8F5F8AF58DB8C7A93F822B89E5C21_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FAE8F5F8AF58DB8C7A93F822B89E5C21" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_884AFAFADA9D707C27F1F822B89D662B" xlink:to="loc_dei_EntityDomain_FAE8F5F8AF58DB8C7A93F822B89E5C21" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_B38095BF2066BB51C9DDF822B89E8FE0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FAE8F5F8AF58DB8C7A93F822B89E5C21" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_B38095BF2066BB51C9DDF822B89E8FE0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_0FE60CC6A52864AA2C11F822B89E20CA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_182FA13BBA7E0CDBA220F822B89BB429" xlink:to="loc_us-gaap_StatementGeographicalAxis_0FE60CC6A52864AA2C11F822B89E20CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_0FE60CC6A52864AA2C11F822B89E20CA" xlink:to="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_0FE60CC6A52864AA2C11F822B89E20CA" xlink:to="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:label="loc_country_US_3EF19C47429395079B66F822B89FFEFC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29" xlink:to="loc_country_US_3EF19C47429395079B66F822B89FFEFC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonUsMember" xlink:label="loc_us-gaap_NonUsMember_F05809C1601D02459EBAF822B89F4059" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_FDF633D20A5E8667316EF822B89ECA29" xlink:to="loc_us-gaap_NonUsMember_F05809C1601D02459EBAF822B89F4059" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_AEE95C726F31B2E965FCF822B89F1021" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_1B245B7F9551DA52DE7DF822B89F7C71" xlink:to="loc_us-gaap_Revenues_AEE95C726F31B2E965FCF822B89F1021" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_B4652187F986E64B380EF822B91612A0" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_F8007DA9B0FAE17DB089F822B915F786" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B4652187F986E64B380EF822B91612A0" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_F8007DA9B0FAE17DB089F822B915F786" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_65940B129C3C61A023E2F822B9150059" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_F8007DA9B0FAE17DB089F822B915F786" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_65940B129C3C61A023E2F822B9150059" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_AA349295A05DE50E09C2F822B91572D1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_65940B129C3C61A023E2F822B9150059" xlink:to="loc_us-gaap_TypeOfAdoptionMember_AA349295A05DE50E09C2F822B91572D1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_AA349295A05DE50E09C2F822B91572D1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_65940B129C3C61A023E2F822B9150059" xlink:to="loc_us-gaap_TypeOfAdoptionMember_AA349295A05DE50E09C2F822B91572D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountingStandardsUpdate201409Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201409Member_270EE82463D303EF8658F822B9159767" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_AA349295A05DE50E09C2F822B91572D1" xlink:to="loc_us-gaap_AccountingStandardsUpdate201409Member_270EE82463D303EF8658F822B9159767" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_B260B371E1C5DD548D2AF822B91536AF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_F8007DA9B0FAE17DB089F822B915F786" xlink:to="loc_dei_LegalEntityAxis_B260B371E1C5DD548D2AF822B91536AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9A5B7582F5665AC1F412F822B9153473_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_B260B371E1C5DD548D2AF822B91536AF" xlink:to="loc_dei_EntityDomain_9A5B7582F5665AC1F412F822B9153473_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9A5B7582F5665AC1F412F822B9153473" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_B260B371E1C5DD548D2AF822B91536AF" xlink:to="loc_dei_EntityDomain_9A5B7582F5665AC1F412F822B9153473" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_1E5A40EF9C05734620CDF822B9165365" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9A5B7582F5665AC1F412F822B9153473" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_1E5A40EF9C05734620CDF822B9165365" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_70E00C320C999F833400F822B916C3CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B4652187F986E64B380EF822B91612A0" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_70E00C320C999F833400F822B916C3CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_3C3BBCACD089689258B1F822B9163BEE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B4652187F986E64B380EF822B91612A0" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_3C3BBCACD089689258B1F822B9163BEE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ScheduleOfOtherBalanceSheetAccountsTableTextBlock" xlink:label="loc_cmcsa_ScheduleOfOtherBalanceSheetAccountsTableTextBlock_B500C1845D9DD8AD07E3F822B9163851" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B4652187F986E64B380EF822B91612A0" xlink:to="loc_cmcsa_ScheduleOfOtherBalanceSheetAccountsTableTextBlock_B500C1845D9DD8AD07E3F822B9163851" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformation" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_CA411B8984D20F2B56A83F8B2628AC83" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_57B41A587E1FB1766B2A3F8B2627B9A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CA411B8984D20F2B56A83F8B2628AC83" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_57B41A587E1FB1766B2A3F8B2627B9A0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_9364029E6246A85B48FF3F8B26279EAB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_57B41A587E1FB1766B2A3F8B2627B9A0" xlink:to="loc_dei_LegalEntityAxis_9364029E6246A85B48FF3F8B26279EAB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C327E592FE020C33CCCF3F8B26284F1B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9364029E6246A85B48FF3F8B26279EAB" xlink:to="loc_dei_EntityDomain_C327E592FE020C33CCCF3F8B26284F1B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C327E592FE020C33CCCF3F8B26284F1B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9364029E6246A85B48FF3F8B26279EAB" xlink:to="loc_dei_EntityDomain_C327E592FE020C33CCCF3F8B26284F1B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_DD445BF2C82037F607833F8B262878B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C327E592FE020C33CCCF3F8B26284F1B" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_DD445BF2C82037F607833F8B262878B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingDisclosureTextBlock" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_8E96A7380A5A8F26CF773F8B2628DD87" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_CA411B8984D20F2B56A83F8B2628AC83" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_8E96A7380A5A8F26CF773F8B2628DD87" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_A5B0035F80106E7FFD0FDB648E94AF4E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_84C95CED6832057EE570DB648E94F451" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_A5B0035F80106E7FFD0FDB648E94AF4E" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_84C95CED6832057EE570DB648E94F451" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_775CFFE4BEDF7262A3D1DB648E943AAD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_84C95CED6832057EE570DB648E94F451" xlink:to="loc_us-gaap_ConsolidationItemsAxis_775CFFE4BEDF7262A3D1DB648E943AAD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_775CFFE4BEDF7262A3D1DB648E943AAD" xlink:to="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_775CFFE4BEDF7262A3D1DB648E943AAD" xlink:to="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingSegmentsMember" xlink:label="loc_us-gaap_OperatingSegmentsMember_BA1C337AA3D8A50F86C3DB648E94CB95" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2" xlink:to="loc_us-gaap_OperatingSegmentsMember_BA1C337AA3D8A50F86C3DB648E94CB95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="loc_us-gaap_CorporateNonSegmentMember_CA93D9828219FE867A44DB648E943157" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2" xlink:to="loc_us-gaap_CorporateNonSegmentMember_CA93D9828219FE867A44DB648E943157" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaterialReconcilingItemsMember" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_43B6779F6D95E46C34BEDB6A5EA53F8E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_C676BB34008D8A75B438DB648E94F8C2" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_43B6779F6D95E46C34BEDB6A5EA53F8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_46B55CA4F54C28B911F7DB648E943EBA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_84C95CED6832057EE570DB648E94F451" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_46B55CA4F54C28B911F7DB648E943EBA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_46B55CA4F54C28B911F7DB648E943EBA" xlink:to="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_46B55CA4F54C28B911F7DB648E943EBA" xlink:to="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_30692358FCCD5488C08ADB648E941457" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_CableCommunicationsMember_30692358FCCD5488C08ADB648E941457" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_CableNetworksMember" xlink:label="loc_cmcsa_CableNetworksMember_C7A00BAF0A08B09E4167DB648E949C54" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_CableNetworksMember_C7A00BAF0A08B09E4167DB648E949C54" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BroadcastTelevisionMember" xlink:label="loc_cmcsa_BroadcastTelevisionMember_92443D38D518DEF3063FDB648E9486B0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_BroadcastTelevisionMember_92443D38D518DEF3063FDB648E9486B0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_FilmedEntertainmentMember" xlink:label="loc_cmcsa_FilmedEntertainmentMember_3885D29AC1F593E1A3F3DB648E94A76A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_FilmedEntertainmentMember_3885D29AC1F593E1A3F3DB648E94A76A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ThemeParksMember" xlink:label="loc_cmcsa_ThemeParksMember_D14F217FA79DF9BF4A2CDB648E94432E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_ThemeParksMember_D14F217FA79DF9BF4A2CDB648E94432E" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalSegmentsMember" xlink:label="loc_cmcsa_NBCUniversalSegmentsMember_66BE90D731727B345FE8DB648E94605F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_BB3699722046B5FE8E75DB648E94D7DA" xlink:to="loc_cmcsa_NBCUniversalSegmentsMember_66BE90D731727B345FE8DB648E94605F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_76690ABF111AEEB54AEADB648E9414C9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_84C95CED6832057EE570DB648E94F451" xlink:to="loc_dei_LegalEntityAxis_76690ABF111AEEB54AEADB648E9414C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_37D2442FAECC9C09B5B4DB648E94FB9C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_76690ABF111AEEB54AEADB648E9414C9" xlink:to="loc_dei_EntityDomain_37D2442FAECC9C09B5B4DB648E94FB9C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_37D2442FAECC9C09B5B4DB648E94FB9C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_76690ABF111AEEB54AEADB648E9414C9" xlink:to="loc_dei_EntityDomain_37D2442FAECC9C09B5B4DB648E94FB9C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_E1C3840ED0B3529B3609DB648E94F7D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_37D2442FAECC9C09B5B4DB648E94FB9C" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_E1C3840ED0B3529B3609DB648E94F7D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NumberOfReportableSegments" xlink:label="loc_us-gaap_NumberOfReportableSegments_1A234A426DD8B572BFEBDB648E94D8BA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_A5B0035F80106E7FFD0FDB648E94AF4E" xlink:to="loc_us-gaap_NumberOfReportableSegments_1A234A426DD8B572BFEBDB648E94D8BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationProfitLossAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_A5B0035F80106E7FFD0FDB648E94AF4E" xlink:to="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_B110BCC1FA3F65709ACBDB648E95DE25" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:to="loc_us-gaap_Revenues_B110BCC1FA3F65709ACBDB648E95DE25" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AdjustedEBITDA" xlink:label="loc_cmcsa_AdjustedEBITDA_F8C52A9A2D53B542DC79DB648E95D645" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:to="loc_cmcsa_AdjustedEBITDA_F8C52A9A2D53B542DC79DB648E95D645" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="loc_us-gaap_DepreciationAndAmortization_B5A2C261D2E8B5421C48DB648E959674" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:to="loc_us-gaap_DepreciationAndAmortization_B5A2C261D2E8B5421C48DB648E959674" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_41F22151E09CB73CA305DB648E956B18" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_41F22151E09CB73CA305DB648E956B18" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_676FD494E813C70521EBDB648E95C13E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_A0D65B21C5684D21F45ADB648E953328" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_676FD494E813C70521EBDB648E95C13E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems" xlink:label="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable" xlink:label="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_4144A460E87DC341997DB0531A2E0327" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_4144A460E87DC341997DB0531A2E0327" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1162D6A1329813750DAAB0531A2EBEE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTable_4144A460E87DC341997DB0531A2E0327" xlink:to="loc_dei_LegalEntityAxis_1162D6A1329813750DAAB0531A2EBEE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DCDBF9F7687181E91781B0531A2E727A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1162D6A1329813750DAAB0531A2EBEE9" xlink:to="loc_dei_EntityDomain_DCDBF9F7687181E91781B0531A2E727A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DCDBF9F7687181E91781B0531A2E727A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1162D6A1329813750DAAB0531A2EBEE9" xlink:to="loc_dei_EntityDomain_DCDBF9F7687181E91781B0531A2E727A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_53AE4BCE166D5C40A19EB0531A2F7B00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DCDBF9F7687181E91781B0531A2E727A" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_53AE4BCE166D5C40A19EB0531A2F7B00" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_AdjustedEBITDA" xlink:label="loc_cmcsa_AdjustedEBITDA_CA8F2F6B6947D6E1B3A8B0531A2FD7EA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_cmcsa_AdjustedEBITDA_CA8F2F6B6947D6E1B3A8B0531A2FD7EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_FDE0115BAEB7FDA5C7F2B0531A2FBB15" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_Depreciation_FDE0115BAEB7FDA5C7F2B0531A2FBB15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_8DD3BDA2D520CEFC3492B0531A2F01CA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_8DD3BDA2D520CEFC3492B0531A2F01CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_56A1A1FC7BAC75475B61B06463EBC4A3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_InterestExpense_56A1A1FC7BAC75475B61B06463EBC4A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_04B2E8D1CD57FA114191B0531A2F2F13" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_04B2E8D1CD57FA114191B0531A2F2F13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_22978294DD7481A1F19FB0531A2FF031" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems_1ECC95FF28AAEF48D4A4B0531A2FAB60" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_22978294DD7481A1F19FB0531A2FF031" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_0065C5CAB13B97B046213F8B2625AD83" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_B532C5B600B033B357D13F8B2625315B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_0065C5CAB13B97B046213F8B2625AD83" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_B532C5B600B033B357D13F8B2625315B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_DCDC9BB1BBA90945459C3F8B262565A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_B532C5B600B033B357D13F8B2625315B" xlink:to="loc_dei_LegalEntityAxis_DCDC9BB1BBA90945459C3F8B262565A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D402779C10BE5F3CC0B63F8B2625166B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_DCDC9BB1BBA90945459C3F8B262565A5" xlink:to="loc_dei_EntityDomain_D402779C10BE5F3CC0B63F8B2625166B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D402779C10BE5F3CC0B63F8B2625166B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_DCDC9BB1BBA90945459C3F8B262565A5" xlink:to="loc_dei_EntityDomain_D402779C10BE5F3CC0B63F8B2625166B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_372D81D2146EA8DD72C93F8B2625AD8B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D402779C10BE5F3CC0B63F8B2625166B" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_372D81D2146EA8DD72C93F8B2625AD8B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_26BCB0590E6B1369FF8C3F8B2625A0A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_0065C5CAB13B97B046213F8B2625AD83" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_26BCB0590E6B1369FF8C3F8B2625A0A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock" xlink:label="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_FD7DA4E2703144B7CFB73F8B2625F099" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_0065C5CAB13B97B046213F8B2625AD83" xlink:to="loc_us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_FD7DA4E2703144B7CFB73F8B2625F099" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SignificantTransactions" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_B215F01815DFDF31B2C0FCD2B82B1AA7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1E163C858BE6330AAFDCFCD2B82BB520" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_B215F01815DFDF31B2C0FCD2B82B1AA7" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1E163C858BE6330AAFDCFCD2B82BB520" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_A3229992CABFD7F0D79AFCD2B82B28DC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1E163C858BE6330AAFDCFCD2B82BB520" xlink:to="loc_dei_LegalEntityAxis_A3229992CABFD7F0D79AFCD2B82B28DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7072F3CC5C091BF18086FCD2B82BA01A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_A3229992CABFD7F0D79AFCD2B82B28DC" xlink:to="loc_dei_EntityDomain_7072F3CC5C091BF18086FCD2B82BA01A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7072F3CC5C091BF18086FCD2B82BA01A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_A3229992CABFD7F0D79AFCD2B82B28DC" xlink:to="loc_dei_EntityDomain_7072F3CC5C091BF18086FCD2B82BA01A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_34A1B42C57258AD30C12FCD2B82BA063" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7072F3CC5C091BF18086FCD2B82BA01A" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_34A1B42C57258AD30C12FCD2B82BA063" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SignificantTransactionsTextBlock" xlink:label="loc_cmcsa_SignificantTransactionsTextBlock_133E1C6B2B4151A23266FCD2B82BC519" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_B215F01815DFDF31B2C0FCD2B82B1AA7" xlink:to="loc_cmcsa_SignificantTransactionsTextBlock_133E1C6B2B4151A23266FCD2B82BC519" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SignificantTransactionsSkyOfferDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_226D84F6468971BAC1B8F8AF896B7BA4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_226D84F6468971BAC1B8F8AF896B7BA4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_19EFAE64CE8183F48127F8AF896B4B4F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_226D84F6468971BAC1B8F8AF896B7BA4" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_19EFAE64CE8183F48127F8AF896B4B4F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_C4F606041964EB9BB97FF8AF896B723A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_19EFAE64CE8183F48127F8AF896B4B4F" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_C4F606041964EB9BB97FF8AF896B723A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_C4F606041964EB9BB97FF8AF896B723A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_19EFAE64CE8183F48127F8AF896B4B4F" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_C4F606041964EB9BB97FF8AF896B723A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_CFB82C3640A2AB3C374FF8AF896B8BF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_C4F606041964EB9BB97FF8AF896B723A" xlink:to="loc_us-gaap_SubsequentEventMember_CFB82C3640A2AB3C374FF8AF896B8BF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_6E01AB1BB40E8812A066F8AF896BEBF4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_226D84F6468971BAC1B8F8AF896B7BA4" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_6E01AB1BB40E8812A066F8AF896BEBF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_BFE86DE033EB80EB3EB9F8AF896B2EB0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6E01AB1BB40E8812A066F8AF896BEBF4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_BFE86DE033EB80EB3EB9F8AF896B2EB0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_BFE86DE033EB80EB3EB9F8AF896B2EB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_6E01AB1BB40E8812A066F8AF896BEBF4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_BFE86DE033EB80EB3EB9F8AF896B2EB0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SkyPLCMember" xlink:label="loc_cmcsa_SkyPLCMember_1991774F10F3442345A4F8AF896B2961" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_BFE86DE033EB80EB3EB9F8AF896B2EB0" xlink:to="loc_cmcsa_SkyPLCMember_1991774F10F3442345A4F8AF896B2961" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAcquisitionCashOfferPerSharePrice" xlink:label="loc_cmcsa_BusinessAcquisitionCashOfferPerSharePrice_8A943D13DF2014C1D6E1F8AF896B29A6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_BusinessAcquisitionCashOfferPerSharePrice_8A943D13DF2014C1D6E1F8AF896B29A6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAcquisitionCashOfferImpliedValue" xlink:label="loc_cmcsa_BusinessAcquisitionCashOfferImpliedValue_A485EF3E40124C2B786CF8AF896B06A9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_BusinessAcquisitionCashOfferImpliedValue_A485EF3E40124C2B786CF8AF896B06A9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAcquisitionCashOfferPerSharePriceMaximumFinalDividendBasedOnFiscalYearEnd" xlink:label="loc_cmcsa_BusinessAcquisitionCashOfferPerSharePriceMaximumFinalDividendBasedOnFiscalYearEnd_A6880C610542572CC711F8AF896B00C0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_BusinessAcquisitionCashOfferPerSharePriceMaximumFinalDividendBasedOnFiscalYearEnd_A6880C610542572CC711F8AF896B00C0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_BusinessAcquisitionsConditionsMinimumAcceptancePercentageOfVotingRights" xlink:label="loc_cmcsa_BusinessAcquisitionsConditionsMinimumAcceptancePercentageOfVotingRights_E1BD8BE249FC4B8DB384F8AF896BA678" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_BusinessAcquisitionsConditionsMinimumAcceptancePercentageOfVotingRights_E1BD8BE249FC4B8DB384F8AF896BA678" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_UnsecuredBridgeCreditAgreementMaximumBorrowingCapacity" xlink:label="loc_cmcsa_UnsecuredBridgeCreditAgreementMaximumBorrowingCapacity_C8A14A0048543B5B7765F8AF896B43A6" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_UnsecuredBridgeCreditAgreementMaximumBorrowingCapacity_C8A14A0048543B5B7765F8AF896B43A6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_UnsecuredTermLoanCreditAgreementMaximumBorrowingCapacity" xlink:label="loc_cmcsa_UnsecuredTermLoanCreditAgreementMaximumBorrowingCapacity_45EB2F0232F28CAFF0A3F8AF896B59C8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_A5C8A4A1B83BCF293E9EF8AF896B95F2" xlink:to="loc_cmcsa_UnsecuredTermLoanCreditAgreementMaximumBorrowingCapacity_45EB2F0232F28CAFF0A3F8AF896B59C8" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SignificantTransactionsUniversalBeijingResortDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityLineItems" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_5D752F44EBF37A6571C6F9DC569A9503" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_5D752F44EBF37A6571C6F9DC569A9503" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_2215B3E91BF052BFCB30F9DC569A48DD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_5D752F44EBF37A6571C6F9DC569A9503" xlink:to="loc_dei_LegalEntityAxis_2215B3E91BF052BFCB30F9DC569A48DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_766749F36F1B91774734F9DC569A4451_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_2215B3E91BF052BFCB30F9DC569A48DD" xlink:to="loc_dei_EntityDomain_766749F36F1B91774734F9DC569A4451_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_766749F36F1B91774734F9DC569A4451" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_2215B3E91BF052BFCB30F9DC569A48DD" xlink:to="loc_dei_EntityDomain_766749F36F1B91774734F9DC569A4451" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_DC0B3DD0F579BC80AB01F9DC569A69CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_766749F36F1B91774734F9DC569A4451" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_DC0B3DD0F579BC80AB01F9DC569A69CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_5E517F3863B05B17340CF9DC569A6D42" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_5D752F44EBF37A6571C6F9DC569A9503" xlink:to="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_5E517F3863B05B17340CF9DC569A6D42" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_BE3F3D329165972097B0F9DC569BF9C5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_5E517F3863B05B17340CF9DC569A6D42" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_BE3F3D329165972097B0F9DC569BF9C5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_BE3F3D329165972097B0F9DC569BF9C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_5E517F3863B05B17340CF9DC569A6D42" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_BE3F3D329165972097B0F9DC569BF9C5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_UniversalBeijingResortMember" xlink:label="loc_cmcsa_UniversalBeijingResortMember_C01D27C4F944E8C6CDC2F9DC569C6C3F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_BE3F3D329165972097B0F9DC569BF9C5" xlink:to="loc_cmcsa_UniversalBeijingResortMember_C01D27C4F944E8C6CDC2F9DC569C6C3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_576755085D4CBD865865F9DC569C424B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_576755085D4CBD865865F9DC569C424B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_VariableInterestEntityMaximumBorrowingCapacity" xlink:label="loc_cmcsa_VariableInterestEntityMaximumBorrowingCapacity_2341D2E98FC6A1FC44C9F9DC569D6694" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:to="loc_cmcsa_VariableInterestEntityMaximumBorrowingCapacity_2341D2E98FC6A1FC44C9F9DC569D6694" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets" xlink:label="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets_FDA16A342A6EDFDE883CF9DC569DDCF9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:to="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets_FDA16A342A6EDFDE883CF9DC569DDCF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities" xlink:label="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities_2A350CAAFDC4F5C7FA76F9DC569DCD74" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_3509EC60C43A6750329CF9DC569C5633" xlink:to="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities_2A350CAAFDC4F5C7FA76F9DC569DCD74" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformation" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationLineItems" xlink:label="loc_cmcsa_SupplementalFinancialInformationLineItems_92314076FD250415E089FC1E36870BB8" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationTable" xlink:label="loc_cmcsa_SupplementalFinancialInformationTable_E55BAC11446C51183D8CFC1E3687A68B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_92314076FD250415E089FC1E36870BB8" xlink:to="loc_cmcsa_SupplementalFinancialInformationTable_E55BAC11446C51183D8CFC1E3687A68B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_67742BC40302E771CC98FC1E368751B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_E55BAC11446C51183D8CFC1E3687A68B" xlink:to="loc_dei_LegalEntityAxis_67742BC40302E771CC98FC1E368751B6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E911FEFB7B2849FA3375FC1E3687E50F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_67742BC40302E771CC98FC1E368751B6" xlink:to="loc_dei_EntityDomain_E911FEFB7B2849FA3375FC1E3687E50F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E911FEFB7B2849FA3375FC1E3687E50F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_67742BC40302E771CC98FC1E368751B6" xlink:to="loc_dei_EntityDomain_E911FEFB7B2849FA3375FC1E3687E50F" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_1375E91F591AFF1F2B31FC1E3687C790" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E911FEFB7B2849FA3375FC1E3687E50F" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_1375E91F591AFF1F2B31FC1E3687C790" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalFinancialInformationDisclosureTextBlock" xlink:label="loc_us-gaap_AdditionalFinancialInformationDisclosureTextBlock_14ACE3E55CE4A4882B55FC1E3687ADFA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_92314076FD250415E089FC1E36870BB8" xlink:to="loc_us-gaap_AdditionalFinancialInformationDisclosureTextBlock_14ACE3E55CE4A4882B55FC1E3687ADFA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationLineItems" xlink:label="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationTable" xlink:label="loc_cmcsa_SupplementalFinancialInformationTable_06614914FC8503B76A6FE37FF5CFC1FF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:to="loc_cmcsa_SupplementalFinancialInformationTable_06614914FC8503B76A6FE37FF5CFC1FF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_B8712C2C1A1FCC14FEA5E37FF5CF5034" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_06614914FC8503B76A6FE37FF5CFC1FF" xlink:to="loc_dei_LegalEntityAxis_B8712C2C1A1FCC14FEA5E37FF5CF5034" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D4E711AA2FF23F81137FE37FF5CF9012_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_B8712C2C1A1FCC14FEA5E37FF5CF5034" xlink:to="loc_dei_EntityDomain_D4E711AA2FF23F81137FE37FF5CF9012_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D4E711AA2FF23F81137FE37FF5CF9012" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_B8712C2C1A1FCC14FEA5E37FF5CF5034" xlink:to="loc_dei_EntityDomain_D4E711AA2FF23F81137FE37FF5CF9012" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_05BA1824D06371A7966DE37FF5D06109" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D4E711AA2FF23F81137FE37FF5CF9012" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_05BA1824D06371A7966DE37FF5D06109" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_E0DF83699088A755F394E37FF5D02B4D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_E0DF83699088A755F394E37FF5D02B4D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashCurrent" xlink:label="loc_us-gaap_RestrictedCashCurrent_112B8CCD2C187A335B42E37FF5D0C370" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:to="loc_us-gaap_RestrictedCashCurrent_112B8CCD2C187A335B42E37FF5D0C370" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashNoncurrent" xlink:label="loc_us-gaap_RestrictedCashNoncurrent_5FAA9781544184022752E37FF5D09787" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:to="loc_us-gaap_RestrictedCashNoncurrent_5FAA9781544184022752E37FF5D09787" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_A28B90DEC7FA9EF0449CE37FF5D09B16" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_8DD4D7B3DB36258275B2E37FF5D07959" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_A28B90DEC7FA9EF0449CE37FF5D09B16" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesdetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationLineItems" xlink:label="loc_cmcsa_SupplementalFinancialInformationLineItems_E6989C6078403CD3F2A8265AAE089C5C" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationTable" xlink:label="loc_cmcsa_SupplementalFinancialInformationTable_A776AE3498A9F48C0FF2265AAE08CB51" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_E6989C6078403CD3F2A8265AAE089C5C" xlink:to="loc_cmcsa_SupplementalFinancialInformationTable_A776AE3498A9F48C0FF2265AAE08CB51" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_EAAC79595A5B935DE95F265AAE082835" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_A776AE3498A9F48C0FF2265AAE08CB51" xlink:to="loc_dei_LegalEntityAxis_EAAC79595A5B935DE95F265AAE082835" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_67073CF85E3590A40C53265AAE08EA3B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_EAAC79595A5B935DE95F265AAE082835" xlink:to="loc_dei_EntityDomain_67073CF85E3590A40C53265AAE08EA3B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_67073CF85E3590A40C53265AAE08EA3B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_EAAC79595A5B935DE95F265AAE082835" xlink:to="loc_dei_EntityDomain_67073CF85E3590A40C53265AAE08EA3B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_580349CB1C537CBA5370265AAE08274C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_67073CF85E3590A40C53265AAE08EA3B" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_580349CB1C537CBA5370265AAE08274C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_DC42EA677BFB74B93470265AAE081F2A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_E6989C6078403CD3F2A8265AAE089C5C" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_DC42EA677BFB74B93470265AAE081F2A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestPaidNet" xlink:label="loc_us-gaap_InterestPaidNet_5D9AF2490E2529261F8D265AAE084AF3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_DC42EA677BFB74B93470265AAE081F2A" xlink:to="loc_us-gaap_InterestPaidNet_5D9AF2490E2529261F8D265AAE084AF3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_3E0505606F9BF42CDC95265AAE082155" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_DC42EA677BFB74B93470265AAE081F2A" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_3E0505606F9BF42CDC95265AAE082155" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_3CE3AE3FAC802BBFA941265AB0A7337B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_3CE3AE3FAC802BBFA941265AB0A7337B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_DBE370C7A26A01AD694B265AB0A77ED2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_3CE3AE3FAC802BBFA941265AB0A7337B" xlink:to="loc_dei_LegalEntityAxis_DBE370C7A26A01AD694B265AB0A77ED2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_EC93472AADBE342A688F265AB0A75891_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_DBE370C7A26A01AD694B265AB0A77ED2" xlink:to="loc_dei_EntityDomain_EC93472AADBE342A688F265AB0A75891_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_EC93472AADBE342A688F265AB0A75891" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_DBE370C7A26A01AD694B265AB0A77ED2" xlink:to="loc_dei_EntityDomain_EC93472AADBE342A688F265AB0A75891" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_8A4255C0348253B0CEE0265AB0A7E456" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_EC93472AADBE342A688F265AB0A75891" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_8A4255C0348253B0CEE0265AB0A7E456" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_636A53AAE66D91CFD8EE265AB0A8C99D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_636A53AAE66D91CFD8EE265AB0A8C99D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax_7A9B3CBAF90356067317265AB0A895E0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax_7A9B3CBAF90356067317265AB0A895E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_CD003226C208A44A5CBD265AB0A820AC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_CD003226C208A44A5CBD265AB0A820AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_AB299A2774A78AEA8261265AB0A81DE6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_AB299A2774A78AEA8261265AB0A81DE6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_67DA4F25198080F1664F265AB0A81D02" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_6E1B005337C9D84F9FB1265AB0A8304C" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_67DA4F25198080F1664F265AB0A81D02" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationNoncashInvestingAndFinancingActivitiesdetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationLineItems" xlink:label="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationTable" xlink:label="loc_cmcsa_SupplementalFinancialInformationTable_7D05602EE0174C85B941DF87FD6DCB5B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:to="loc_cmcsa_SupplementalFinancialInformationTable_7D05602EE0174C85B941DF87FD6DCB5B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_0B4C508B9FF2C83D0339DF87FD6DED92" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_7D05602EE0174C85B941DF87FD6DCB5B" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_0B4C508B9FF2C83D0339DF87FD6DED92" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_49E60BDA1D68AFC222BDDF87FD6D2DD1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_0B4C508B9FF2C83D0339DF87FD6DED92" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_49E60BDA1D68AFC222BDDF87FD6D2DD1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMethodInvesteeNameDomain" xlink:label="loc_us-gaap_EquityMethodInvesteeNameDomain_49E60BDA1D68AFC222BDDF87FD6D2DD1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_0B4C508B9FF2C83D0339DF87FD6DED92" xlink:to="loc_us-gaap_EquityMethodInvesteeNameDomain_49E60BDA1D68AFC222BDDF87FD6D2DD1" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_UniversalBeijingResortMember" xlink:label="loc_cmcsa_UniversalBeijingResortMember_550EF3042A527BBF5A63DF87FD6D88C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvesteeNameDomain_49E60BDA1D68AFC222BDDF87FD6D2DD1" xlink:to="loc_cmcsa_UniversalBeijingResortMember_550EF3042A527BBF5A63DF87FD6D88C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_BB07A4099F2FACE281B9DF87FD6DB56B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_7D05602EE0174C85B941DF87FD6DCB5B" xlink:to="loc_dei_LegalEntityAxis_BB07A4099F2FACE281B9DF87FD6DB56B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_ACA9A93D3B2478380A05DF87FD6D120A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_BB07A4099F2FACE281B9DF87FD6DB56B" xlink:to="loc_dei_EntityDomain_ACA9A93D3B2478380A05DF87FD6D120A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_ACA9A93D3B2478380A05DF87FD6D120A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_BB07A4099F2FACE281B9DF87FD6DB56B" xlink:to="loc_dei_EntityDomain_ACA9A93D3B2478380A05DF87FD6D120A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_8D89171093826ADAB9CEDF87FD6D968E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ACA9A93D3B2478380A05DF87FD6D120A" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_8D89171093826ADAB9CEDF87FD6D968E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_19C02044EFABE5399C80DF87FD6D2F51" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_19C02044EFABE5399C80DF87FD6D2F51" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_FF5B8213E9A9703A1B9BDF87FD6D5E98" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_FF5B8213E9A9703A1B9BDF87FD6D5E98" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DividendsPayableAmountPerShare" xlink:label="loc_us-gaap_DividendsPayableAmountPerShare_24D5C9F3843E07693208DF87FD6D46A7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:to="loc_us-gaap_DividendsPayableAmountPerShare_24D5C9F3843E07693208DF87FD6D46A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContributionOfProperty" xlink:label="loc_us-gaap_ContributionOfProperty_0B0B7D9A42D558B4956FDF87FD6D1436" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_2D45EA5D039B1BDCDC21DF87FD6D0F8E" xlink:to="loc_us-gaap_ContributionOfProperty_0B0B7D9A42D558B4956FDF87FD6D1436" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationShareBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B09C19B0EDCD69C0CA14E3B06CC1D83C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B09C19B0EDCD69C0CA14E3B06CC1D83C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_2C3C6084430C1A253125E3B06CC1FABE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B09C19B0EDCD69C0CA14E3B06CC1D83C" xlink:to="loc_us-gaap_PlanNameAxis_2C3C6084430C1A253125E3B06CC1FABE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_D24C0FCDD21B577DDC9AE3B06CC14BCC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_2C3C6084430C1A253125E3B06CC1FABE" xlink:to="loc_us-gaap_PlanNameDomain_D24C0FCDD21B577DDC9AE3B06CC14BCC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_D24C0FCDD21B577DDC9AE3B06CC14BCC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_2C3C6084430C1A253125E3B06CC1FABE" xlink:to="loc_us-gaap_PlanNameDomain_D24C0FCDD21B577DDC9AE3B06CC14BCC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ManagementGrantMember" xlink:label="loc_cmcsa_ManagementGrantMember_C98CB7F966B1F9D4C9A0E3B06CC10B22" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_D24C0FCDD21B577DDC9AE3B06CC14BCC" xlink:to="loc_cmcsa_ManagementGrantMember_C98CB7F966B1F9D4C9A0E3B06CC10B22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_C131484195C557EC4E9EE3B06CC2CABF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_B09C19B0EDCD69C0CA14E3B06CC1D83C" xlink:to="loc_us-gaap_AwardTypeAxis_C131484195C557EC4E9EE3B06CC2CABF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_C131484195C557EC4E9EE3B06CC2CABF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_C131484195C557EC4E9EE3B06CC2CABF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_1B7EA77038385A7C29B2E3B06CC2FEEE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_1B7EA77038385A7C29B2E3B06CC2FEEE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7D22833E816830DEF776E3B06CC2C16D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7D22833E816830DEF776E3B06CC2C16D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_50BAF64E81EC36785F7FE3B06CC258BC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7A422E036FD392D91A5EE3B06CC24693" xlink:to="loc_us-gaap_EmployeeStockMember_50BAF64E81EC36785F7FE3B06CC258BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_FE59ECEE9EEB600ADAB5E3B06CC2C902" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_FE59ECEE9EEB600ADAB5E3B06CC2C902" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_0A6CFF49E1E751BB371EE3B06CC2D16C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_0A6CFF49E1E751BB371EE3B06CC2D16C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5FD31CC7E1B6943F3A06E3B06CC2065B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5FD31CC7E1B6943F3A06E3B06CC2065B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_D875CCC4919EE4910AE5E3B06CC2853A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_D875CCC4919EE4910AE5E3B06CC2853A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_041929716A4D7F6EB19DE3B06CC222B7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_041929716A4D7F6EB19DE3B06CC222B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_06D82F86791761117203E3B06CC298A7" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E4122939069A2B074981E3B06CC2D190" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_06D82F86791761117203E3B06CC298A7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationTables" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationLineItems" xlink:label="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_SupplementalFinancialInformationTable" xlink:label="loc_cmcsa_SupplementalFinancialInformationTable_9215594CA7BF5B3A0F87FDD73416F02C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:to="loc_cmcsa_SupplementalFinancialInformationTable_9215594CA7BF5B3A0F87FDD73416F02C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1856CE58022E64779F18FDD73417BFAB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_SupplementalFinancialInformationTable_9215594CA7BF5B3A0F87FDD73416F02C" xlink:to="loc_dei_LegalEntityAxis_1856CE58022E64779F18FDD73417BFAB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5A1A2AAE74327E773371FDD734171FA3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1856CE58022E64779F18FDD73417BFAB" xlink:to="loc_dei_EntityDomain_5A1A2AAE74327E773371FDD734171FA3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5A1A2AAE74327E773371FDD734171FA3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1856CE58022E64779F18FDD73417BFAB" xlink:to="loc_dei_EntityDomain_5A1A2AAE74327E773371FDD734171FA3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_NBCUniversalMediaLLCMember" xlink:label="loc_cmcsa_NBCUniversalMediaLLCMember_4896E6B173E3996E92A1FDD73417F5A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5A1A2AAE74327E773371FDD734171FA3" xlink:to="loc_cmcsa_NBCUniversalMediaLLCMember_4896E6B173E3996E92A1FDD73417F5A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_7FBF1BEBA4F5E1EE5C78FDD73417122D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:to="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_7FBF1BEBA4F5E1EE5C78FDD73417122D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_6C19BB75376F822E22EFFDD73418A52D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:to="loc_us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_6C19BB75376F822E22EFFDD73418A52D" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20180331.xsd#cmcsa_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" xlink:label="loc_cmcsa_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_7345BB393CCF05811024FDD734183803" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:to="loc_cmcsa_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock_7345BB393CCF05811024FDD734183803" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_97D1EBE01E10B374F865FDD734180DD0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_SupplementalFinancialInformationLineItems_4BBCFB68005813B7007BFDD73417BFE7" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_97D1EBE01E10B374F865FDD734180DD0" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
