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  <xsd:element id="biib_CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear" name="CurrentProvisionsToProductRevenueReservesRelatingToSalesInCurrentYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_DebtInstrumentUnamortizedInterestOnDebt" name="DebtInstrumentUnamortizedInterestOnDebt" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_DecreaseInShareOfCoPromotionProfitsDueToEstimatedCompensationDamages" name="DecreaseInShareOfCoPromotionProfitsDueToEstimatedCompensationDamages" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_DeferredCompensationPlanMember" name="DeferredCompensationPlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_DeferredTaxAssetsCapitalizedCosts" name="DeferredTaxAssetsCapitalizedCosts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_DeferredTaxAssetsIntangibleNet" name="DeferredTaxAssetsIntangibleNet" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_DeferredTaxLiabilitiesDepreciationAmortizationOther" name="DeferredTaxLiabilitiesDepreciationAmortizationOther" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_DeferredTaxLiabilitiesUnrealizedGainOnInvestmentsAndCumulativeTranslationAdjustment" name="DeferredTaxLiabilitiesUnrealizedGainOnInvestmentsAndCumulativeTranslationAdjustment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_DeferredTaxLiabilityRecognized" name="DeferredTaxLiabilityRecognized" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_DenominatorAbstract" name="DenominatorAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_DerecognitionOfConstructionInProgressAssets" name="DerecognitionOfConstructionInProgressAssets" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_DevelopmentExpenseIncurredByCollaborationExcludingUpfrontAndMilestonePayments" name="DevelopmentExpenseIncurredByCollaborationExcludingUpfrontAndMilestonePayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_DirectorsPlanMember" name="DirectorsPlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_DiscountRateRecognizedInCompensationExpense" name="DiscountRateRecognizedInCompensationExpense" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_DistributorOneMember" name="DistributorOneMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_DistributorTwoMember" name="DistributorTwoMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_DueFromUnconsolidatedJointBusiness" name="DueFromUnconsolidatedJointBusiness" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_EachAdditionalOneBillionUpToTwentyBillionMember" name="EachAdditionalOneBillionUpToTwentyBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EachAdditionalSalesLevel" name="EachAdditionalSalesLevel" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_EarningsPerShareTextualAbstract" name="EarningsPerShareTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EffectiveIncomeTaxRateReconciliationContingentConsideration" name="EffectiveIncomeTaxRateReconciliationContingentConsideration" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EffectiveIncomeTaxRateReconciliationManufacturingDeduction" name="EffectiveIncomeTaxRateReconciliationManufacturingDeduction" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EisaiMember" name="EisaiMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ElanMember" name="ElanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EmployeeBenefitPlansTextualAbstract" name="EmployeeBenefitPlansTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EntityWidePercentageOfRevenueFromMajorDistributors" name="EntityWidePercentageOfRevenueFromMajorDistributors" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EquityMethodInvestmentOwnershipPercentageMaximum" name="EquityMethodInvestmentOwnershipPercentageMaximum" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_EquityTextualAbstract" name="EquityTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EstimateOfAdditionalAmountsToBeIncurredInProductDevelopment" name="EstimateOfAdditionalAmountsToBeIncurredInProductDevelopment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones" name="EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_EstimatedTaxLiabilityOnUndistributedEarningsOfForeignSubsidiaries" name="EstimatedTaxLiabilityOnUndistributedEarningsOfForeignSubsidiaries" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_EstimatedUsefulLivesOfLeaseholdImprovements" name="EstimatedUsefulLivesOfLeaseholdImprovements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_EstimatesOfCompensatoryDamagesAndInterest" name="EstimatesOfCompensatoryDamagesAndInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ExpectedAdditionalMilestonePaymentsOnSuccessfulAchievementOfRegulatoryAndCommercialSalesMilestones" name="ExpectedAdditionalMilestonePaymentsOnSuccessfulAchievementOfRegulatoryAndCommercialSalesMilestones" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpectedAdditionalMilestonePaymentsWhenMeetingCertainSalesThreshold" name="ExpectedAdditionalMilestonePaymentsWhenMeetingCertainSalesThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpectedLicenseFeeAndRegulatoryMilestonePayments" name="ExpectedLicenseFeeAndRegulatoryMilestonePayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpenseForNonIncomeBasedStateTaxes" name="ExpenseForNonIncomeBasedStateTaxes" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_ExpenseIncurredByCollaboration" name="ExpenseIncurredByCollaboration" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_ExpenseReflectedWithinStatementsOfIncome" name="ExpenseReflectedWithinStatementsOfIncome" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FacilityLocationAxis" name="FacilityLocationAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FacilityLocationDomain" name="FacilityLocationDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_FairValueInProcessResearchAndDevelopmentDiscountRate" name="FairValueInProcessResearchAndDevelopmentDiscountRate" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainIncludedInEarnings" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainIncludedInEarnings" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLossIncludedInEarnings" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLossIncludedInEarnings" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FinancialInstrumentsTextualAbstract" name="FinancialInstrumentsTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_FinancingArrangementsMember" name="FinancingArrangementsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Finitelivedintangibleassetsfutureamortization" name="Finitelivedintangibleassetsfutureamortization" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_FiveHundredMillionMember" name="FiveHundredMillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FiveHundredMillionToOneBillionMember" name="FiveHundredMillionToOneBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ForeignSalesRequiredToTriggerMilestone" name="ForeignSalesRequiredToTriggerMilestone" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_FumapharmAgMember" name="FumapharmAgMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed20Billion" name="FutureContingentPaymentForAnnualWorldwideNetSalesThatExceed20Billion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureContingentPaymentForAnnualWorldwideNetSalesUpTo20Billion" name="FutureContingentPaymentForAnnualWorldwideNetSalesUpTo20Billion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureContingentPaymentForFirst12Months" name="FutureContingentPaymentForFirst12Months" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureContingentPaymentThreshold" name="FutureContingentPaymentThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_FutureRoyaltiesPercentageToBeReceivedOnSaleOfProduct" name="FutureRoyaltiesPercentageToBeReceivedOnSaleOfProduct" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Futurepercentageofcopromotionoperatingprofits" name="Futurepercentageofcopromotionoperatingprofits" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GAZYVAMember" name="GAZYVAMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_GainLossFromSaleOfStrategicEquityInvestments" name="GainLossFromSaleOfStrategicEquityInvestments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_GainLossRecognizedDuringAcquisitionRelatingToPreExistingEquityInterest" name="GainLossRecognizedDuringAcquisitionRelatingToPreExistingEquityInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_GainOnSaleOfRights" name="GainOnSaleOfRights" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GainOnSaleOfRightsAbstract" name="GainOnSaleOfRightsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_GainOnSaleOfRightsTextBlock" name="GainOnSaleOfRightsTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GenentechMember" name="GenentechMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GermanPlanMember" name="GermanPlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GovernmentSecuritiesCurrentMember" name="GovernmentSecuritiesCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GovernmentSecuritiesNonCurrentMember" name="GovernmentSecuritiesNonCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_GreaterThanThreeBillionMember" name="GreaterThanThreeBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_HillerodDenmarkFacilityMember" name="HillerodDenmarkFacilityMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_HoechstMember" name="HoechstMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ImpairmentChargesRelatedToInvestmentsInPrivatelyHeldCompanies" name="ImpairmentChargesRelatedToInvestmentsInPrivatelyHeldCompanies" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_InLicensedPatentsMember" name="InLicensedPatentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IncomeTaxesTextualAbstract" name="IncomeTaxesTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_IncreasedCarryingAmountOfSeniorNotes" name="IncreasedCarryingAmountOfSeniorNotes" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_IndefiniteLivedIntangibleAssetsUsefulLife" name="IndefiniteLivedIntangibleAssetsUsefulLife" nillable="true" substitutionGroup="xbrli:item" type="us-types:durationStringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IntangibleAssetsAndGoodwillAdditionalTextualAbstract" name="IntangibleAssetsAndGoodwillAdditionalTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_IntangibleAssetsExcludingGoodwillTableTextBlock" name="IntangibleAssetsExcludingGoodwillTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InterestInSubsidiary" name="InterestInSubsidiary" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InventoryVariousProgramsGross" name="InventoryVariousProgramsGross" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_Inventoryreclassification" name="Inventoryreclassification" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities" name="InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_InvestmentInVariableInterestEntitiesTextualAbstract" name="InvestmentInVariableInterestEntitiesTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InvestmentsByThirdPartyInJointVentureAsPerAgreement" name="InvestmentsByThirdPartyInJointVentureAsPerAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_InvestmentsInVariableInterestEntitiesAbstract" name="InvestmentsInVariableInterestEntitiesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_InvestmentsInVariableInterestEntitiesTextBlock" name="InvestmentsInVariableInterestEntitiesTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_IsisPharmaceuticalsMember" name="IsisPharmaceuticalsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_JointVentureOwnerShipPercentageByThirdParty" name="JointVentureOwnerShipPercentageByThirdParty" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_KnoppMember" name="KnoppMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_LessThanFiveHundredMillionMember" name="LessThanFiveHundredMillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_LicenseFee" name="LicenseFee" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_LimitedPeriodForGovernmentReimbursement" name="LimitedPeriodForGovernmentReimbursement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_LitigationAbstract" name="LitigationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_LossContingencyExpectedSettlement" name="LossContingencyExpectedSettlement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_MajorDistributorAxis" name="MajorDistributorAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MajorDistributorDomain" name="MajorDistributorDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketStockUnitsActivityAbstract" name="MarketStockUnitsActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketStockUnitsMember" name="MarketStockUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MarketableEquitySecuritiesMember" name="MarketableEquitySecuritiesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MaximumPercentageOfEarningsOfTargetNumberOfSharesGrantedIfMaximumThresholdLimitIsAttained" name="MaximumPercentageOfEarningsOfTargetNumberOfSharesGrantedIfMaximumThresholdLimitIsAttained" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MaximumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" name="MaximumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MaximumTermForAccountsReceivable" name="MaximumTermForAccountsReceivable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MilestonePaymentDueOnPrior12MonthSales" name="MilestonePaymentDueOnPrior12MonthSales" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_MilestonePaymentsMadeDuringPeriod" name="MilestonePaymentsMadeDuringPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_MilestonesPaymentsMadeToCollaborativePartners" name="MilestonesPaymentsMadeToCollaborativePartners" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_MinimumQualifyingAgeForEmployeeBenefitPlan" name="MinimumQualifyingAgeForEmployeeBenefitPlan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MinimumRentalCommitmentsUnderNoncancellableLeasesAbstract" name="MinimumRentalCommitmentsUnderNoncancellableLeasesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MinimumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" name="MinimumTargetNumberOfMarketStockUnitsGrantedBasedOnStockPerformanceInPercent" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_MinimumTermForAccountsReceivable" name="MinimumTermForAccountsReceivable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MortgageAndOtherAssetBackedSecuritiesCurrentMember" name="MortgageAndOtherAssetBackedSecuritiesCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_MortgageAndOtherAssetBackedSecuritiesNonCurrentMember" name="MortgageAndOtherAssetBackedSecuritiesNonCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NetBenefitForPreviouslyUnrecognizedPosition" name="NetBenefitForPreviouslyUnrecognizedPosition" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetIncomeLossAttributableToNoncontrollingInterestPercentage" name="NetIncomeLossAttributableToNoncontrollingInterestPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NetInterestExpenseBenefit" name="NetInterestExpenseBenefit" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_NetMinimumLeasePayments" name="NetMinimumLeasePayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsThereafter" name="NetMinimumLeasePaymentsThereafter" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInFiveYear" name="NetMinimumLeasePaymentsWithInFiveYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInFourYear" name="NetMinimumLeasePaymentsWithInFourYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInOneYear" name="NetMinimumLeasePaymentsWithInOneYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInThreeYear" name="NetMinimumLeasePaymentsWithInThreeYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_NetMinimumLeasePaymentsWithInTwoYear" name="NetMinimumLeasePaymentsWithInTwoYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_NeurimmuneMember" name="NeurimmuneMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NewAntiCd20Member" name="NewAntiCd20Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NotesPayableToFumedicaMember" name="NotesPayableToFumedicaMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfDaysForCalculationOfAverageClosingStockPrice" name="NumberOfDaysForCalculationOfAverageClosingStockPrice" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfEqualAnnualIncrements" name="NumberOfEqualAnnualIncrements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfShareBasedCompensationPlansPursuantToWhichAwardsAreCurrentlyBeingMade" name="NumberOfShareBasedCompensationPlansPursuantToWhichAwardsAreCurrentlyBeingMade" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfShareBasedCompensationPlansPursuantToWhichNoFurtherAwardsWillBeMade" name="NumberOfShareBasedCompensationPlansPursuantToWhichNoFurtherAwardsWillBeMade" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfSharesOfCommonStockForIssuance" name="NumberOfSharesOfCommonStockForIssuance" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_NumberOfStrategicInvestmentsSold" name="NumberOfStrategicInvestmentsSold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_NumeratorAbstract" name="NumeratorAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OcrelizumabMember" name="OcrelizumabMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OmnibusPlansMember" name="OmnibusPlansMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OneBillionMember" name="OneBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OneBillionToOnePointFiveBillionMember" name="OneBillionToOnePointFiveBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OnePointFiveBillionToTwoBillionMember" name="OnePointFiveBillionToTwoBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_OtherAccruedExpensesAndOther" name="OtherAccruedExpensesAndOther" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_OtherComprehensiveIncomeLossBeforeReclassificationsMember" name="OtherComprehensiveIncomeLossBeforeReclassificationsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_OtherGoodwillAdjustments" name="OtherGoodwillAdjustments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OtherIncomeExpenseMember" name="OtherIncomeExpenseMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_OtherIncomeExpenseNet" name="OtherIncomeExpenseNet" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OtherLiabilitiesNonCurrentMember" name="OtherLiabilitiesNonCurrentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_OtherPaymentsToNoncontrollingInterestsNetOfTax" name="OtherPaymentsToNoncontrollingInterestsNetOfTax" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OtherproductsMember" name="OtherproductsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OtherresearchanddiscoveryMember" name="OtherresearchanddiscoveryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_OutLicensedPatentsMember" name="OutLicensedPatentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentTermsOfAccountsReceivable" name="PaymentTermsOfAccountsReceivable" nillable="true" substitutionGroup="xbrli:item" type="us-types:durationStringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentsForAcquisitionOfNoncontrollingInterest" name="PaymentsForAcquisitionOfNoncontrollingInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear" name="PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToCurrentYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear" name="PaymentsReturnsAppliedAgainstProductRevenueReservesRelatingToPriorYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingLosses" name="PercentageOfCoPromotionOperatingLosses" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsFirstFiftyMillion" name="PercentageOfCoPromotionOperatingProfitsFirstFiftyMillion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillion" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillion" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionOne" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionOne" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoAbstract" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionOne" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionOne" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionThree" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionThree" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionTwo" name="PercentageOfCoPromotionOperatingProfitsGreaterThanFirstFiftyMillionOptionTwoSubOptionTwo" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageOfDevelopmentAndCommercializationExpensesPayableRelated" name="PercentageOfDevelopmentAndCommercializationExpensesPayableRelated" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfDevelopmentReimbursementExpenses" name="PercentageOfDevelopmentReimbursementExpenses" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfMarketValuePerShareOfCommonStock" name="PercentageOfMarketValuePerShareOfCommonStock" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfMinimumInvestmentReturn" name="PercentageOfMinimumInvestmentReturn" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfOperationsOfJointVentureInvestmentsReflectedInConsolidatedFinancialStatements" name="PercentageOfOperationsOfJointVentureInvestmentsReflectedInConsolidatedFinancialStatements" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfRedemptionOfNotes" name="PercentageOfRedemptionOfNotes" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfReimbursementExpenses" name="PercentageOfReimbursementExpenses" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfRoyaltiesAsPerCollaboration" name="PercentageOfRoyaltiesAsPerCollaboration" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PercentageOfVentureCapitalInvestmentsToAssets" name="PercentageOfVentureCapitalInvestmentsToAssets" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageParValueOfSeniorNotes" name="PercentageParValueOfSeniorNotes" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_PercentageReceivablesOfWholesaleDistributorAccountedInConsolidatedReceivables" name="PercentageReceivablesOfWholesaleDistributorAccountedInConsolidatedReceivables" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PerformanceVestedRestrictedStockUnitsActivityAbstract" name="PerformanceVestedRestrictedStockUnitsActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PerformanceVestedRestrictedStockUnitsActivityTableTextBlock" name="PerformanceVestedRestrictedStockUnitsActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_PerformanceVestedRestrictedStockUnitsMember" name="PerformanceVestedRestrictedStockUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_PerformanceVestedRestrictedStockUnitsSettledInSharesMember" name="PerformanceVestedRestrictedStockUnitsSettledInSharesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PeriodForGrantingOfApprovalByApprovingAuthority" name="PeriodForGrantingOfApprovalByApprovingAuthority" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PeriodOfCollaborationAgreement" name="PeriodOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PlanAssetsForDeferredCompensationFairValueDisclosure" name="PlanAssetsForDeferredCompensationFairValueDisclosure" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_PortolaPharmaceuticalsMember" name="PortolaPharmaceuticalsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" name="PotentialFutureMilestonePaymentsCommitmentToThirdPartyApproximately" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_PrejudgmentInterest" name="PrejudgmentInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PresentValueOfNotesPayable" name="PresentValueOfNotesPayable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_PretaxProfitSharingFormulaTableTextBlock" name="PretaxProfitSharingFormulaTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_PriorTwelveMonthSalesAxis" name="PriorTwelveMonthSalesAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_PriorTwelveMonthSalesDomain" name="PriorTwelveMonthSalesDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ProceedsFromMarketableDebtSecuritiesAbstract" name="ProceedsFromMarketableDebtSecuritiesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ProceedsFromMarketableDebtSecuritiesTableTextBlock" name="ProceedsFromMarketableDebtSecuritiesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ProductRevenueReserves" name="ProductRevenueReserves" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_ProductRevenueReservesClassifiedAsReductionOfAccountsReceivable" name="ProductRevenueReservesClassifiedAsReductionOfAccountsReceivable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_ProductRevenueReservesClassifiedAsReductionOfCurrentLiabilities" name="ProductRevenueReservesClassifiedAsReductionOfCurrentLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_ProposedDisallowanceByTaxAuthoritiesForPaymentForServices" name="ProposedDisallowanceByTaxAuthoritiesForPaymentForServices" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ProteostasisTherapeuticsMember" name="ProteostasisTherapeuticsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PurchaseConsiderationForVariableInterestEntities" name="PurchaseConsiderationForVariableInterestEntities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_PurchaseOfCommonSharesInVariableInterestEntities" name="PurchaseOfCommonSharesInVariableInterestEntities" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_PurchasePriceOfCommonStockUnderEspp" name="PurchasePriceOfCommonStockUnderEspp" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RateDuringReimbursementPeriod" name="RateDuringReimbursementPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RatePriorToFirstCommercialSale" name="RatePriorToFirstCommercialSale" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RatioOfNumberOfSharesReservedUnderPlan" name="RatioOfNumberOfSharesReservedUnderPlan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementCostAchievingPeriod" name="ReimbursementCostAchievingPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementLimitStatedInResolution" name="ReimbursementLimitStatedInResolution" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementOfSellingAndDevelopmentExpenses" name="ReimbursementOfSellingAndDevelopmentExpenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ReimbursementUnderAmendedAgreementAmountsPayableAbstract" name="ReimbursementUnderAmendedAgreementAmountsPayableAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementUnderAmendedAgreementAmountsPayableTableTextBlock" name="ReimbursementUnderAmendedAgreementAmountsPayableTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementUnderAmendedAgreementMethod" name="ReimbursementUnderAmendedAgreementMethod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementsOfResearchAndDevelopmentsExpenseFromCollaborationPartner" name="ReimbursementsOfResearchAndDevelopmentsExpenseFromCollaborationPartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_ReimbursementsOfSellingGeneralAndAdministrativeExpensesFromCollaborationPartner" name="ReimbursementsOfSellingGeneralAndAdministrativeExpensesFromCollaborationPartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_RemainingObligationOfFinancingArrangements" name="RemainingObligationOfFinancingArrangements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_RemainingPotentialDevelopmentMilestonePaymentsAndRoyaltiesOnCommercialSalesUnderTermsOfCollaborationAgreement" name="RemainingPotentialDevelopmentMilestonePaymentsAndRoyaltiesOnCommercialSalesUnderTermsOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_ResearchAndDevelopmentCostInSupportOfCollaborationAgreement" name="ResearchAndDevelopmentCostInSupportOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ReservesForDiscountsAndAllowancesAbstract" name="ReservesForDiscountsAndAllowancesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ReservesTextBlock" name="ReservesTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RestOfWorldMember" name="RestOfWorldMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RestrictedStockUnitsActivityAbstract" name="RestrictedStockUnitsActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RetirementOfCommonStock" name="RetirementOfCommonStock" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_RetirementOfCommonStockShares" name="RetirementOfCommonStockShares" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenueRelatedRebates" name="RevenueRelatedRebates" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_Revenuereservesreclassification" name="Revenuereservesreclassification" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesFromUnconsolidatedJointBusiness" name="RevenuesFromUnconsolidatedJointBusiness" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RevenuesFromUnconsolidatedJointBusinessAbstract" name="RevenuesFromUnconsolidatedJointBusinessAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesFromUnconsolidatedJointBusinessTableTextBlock" name="RevenuesFromUnconsolidatedJointBusinessTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RevenuesInPercentageFromUnconsolidatedJointBusiness" name="RevenuesInPercentageFromUnconsolidatedJointBusiness" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RituxanMember" name="RituxanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RocheGroupGenentechMember" name="RocheGroupGenentechMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RoyaltiesTermsOfCollaborationAgreement" name="RoyaltiesTermsOfCollaborationAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RoyaltyAndNetRevenueShareRatesByTerritoryAxis" name="RoyaltyAndNetRevenueShareRatesByTerritoryAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_RoyaltyAndNetRevenueShareRatesByTerritoryDomain" name="RoyaltyAndNetRevenueShareRatesByTerritoryDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RoyaltyCostofSalesPolicyTextBlock" name="RoyaltyCostofSalesPolicyTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_RoyaltyPeriodForSubstantiallyAllRemainingRoyaltyBearingSalesRestOfWorld" name="RoyaltyPeriodForSubstantiallyAllRemainingRoyaltyBearingSalesRestOfWorld" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SalesLevel" name="SalesLevel" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_SalesTriggerGrossSalesThreshold" name="SalesTriggerGrossSalesThreshold" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SamsungBiosimilarAgreementMember" name="SamsungBiosimilarAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SangamoBioSciencesMember" name="SangamoBioSciencesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SavingsPlanMember" name="SavingsPlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfAccountsReceivableFromProductSalesInForeignCountriesTableTextBlock" name="ScheduleOfAccountsReceivableFromProductSalesInForeignCountriesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfCashSettledPerformanceSharesActivityTableTextBlock" name="ScheduleOfCashSettledPerformanceSharesActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ScheduleOfDevelopmentMilestoneAndCollaborationLineItems" name="ScheduleOfDevelopmentMilestoneAndCollaborationLineItems" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ScheduleOfDevelopmentMilestoneAndCollaborationTable" name="ScheduleOfDevelopmentMilestoneAndCollaborationTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfMarketStockUnitsActivityTableTextBlock" name="ScheduleOfMarketStockUnitsActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfMilestonePaymentsBasedOnAttainmentOfCertainSalesLevelsTableTextBlock" name="ScheduleOfMilestonePaymentsBasedOnAttainmentOfCertainSalesLevelsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ScheduleOfPropertyPlantAndEquipmentUsefulLivesTableTextBlock" name="ScheduleOfPropertyPlantAndEquipmentUsefulLivesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SegmentGeographicalGroupsOfCountriesGroupOtherMember" name="SegmentGeographicalGroupsOfCountriesGroupOtherMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SegmentInformationTextualAbstract" name="SegmentInformationTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SellingPriceOfStrategicInvestments" name="SellingPriceOfStrategicInvestments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_SeniorNotesOneMember" name="SeniorNotesOneMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember" name="SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SeniorNotesSixPointZeroPercentDueTwentyThirteenMember" name="SeniorNotesSixPointZeroPercentDueTwentyThirteenMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SeniorNotesTwoMember" name="SeniorNotesTwoMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SeriesXPreferredStockMember" name="SeriesXPreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm" name="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm" name="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_ShareBasedCompensationExpenseIncludedInCostsAndExpenses" name="ShareBasedCompensationExpenseIncludedInCostsAndExpenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedCompensationPlanAxis" name="ShareBasedCompensationPlanAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedCompensationPlanDomain" name="ShareBasedCompensationPlanDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ShareBasedPaymentsTextualAbstract" name="ShareBasedPaymentsTextualAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ShareOfCoPromotionProfits" name="ShareOfCoPromotionProfits" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SharesIssuedUnderEmployeeStockPurchasePlanAbstract" name="SharesIssuedUnderEmployeeStockPurchasePlanAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SharesIssuedUnderEmployeeStockPurchasePlanTableTextBlock" name="SharesIssuedUnderEmployeeStockPurchasePlanTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SobiRateToBiogenOnNetSalesInSobiTerritoryMember" name="SobiRateToBiogenOnNetSalesInSobiTerritoryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SobiTerritoryMember" name="SobiTerritoryMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StockOptionActivityAbstract" name="StockOptionActivityAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StockOptionsAndEmployeeStockPurchasePlanMember" name="StockOptionsAndEmployeeStockPurchasePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_StrategicInvestmentPortfolio" name="StrategicInvestmentPortfolio" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_StrategicInvestmentsMember" name="StrategicInvestmentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StromedixMember" name="StromedixMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_StxOneHundredMember" name="StxOneHundredMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyFiveAbstract" name="SummaryOfActivityRelatedToCollaborationWithCompanyFiveAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyFiveTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyFiveTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyFourAbstract" name="SummaryOfActivityRelatedToCollaborationWithCompanyFourAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyFourTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyFourTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyOneAbstract" name="SummaryOfActivityRelatedToCollaborationWithCompanyOneAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyOneAlongWithEstimateOfAdditionalFutureDevelopmentTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyOneAlongWithEstimateOfAdditionalFutureDevelopmentTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyOneTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyOneTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfActivityRelatedToCollaborationWithCompanySevenAbstract" name="SummaryOfActivityRelatedToCollaborationWithCompanySevenAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanySevenTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanySevenTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfActivityRelatedToCollaborationWithCompanyThreeTableTextBlock" name="SummaryOfActivityRelatedToCollaborationWithCompanyThreeTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfCommonStockTableTextBlock" name="SummaryOfCommonStockTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfFairAndCarryingValueOfDebtInstrumentsAbstract" name="SummaryOfFairAndCarryingValueOfDebtInstrumentsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfPreferredStockTableTextBlock" name="SummaryOfPreferredStockTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsAbstract" name="SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsTableTextBlock" name="SummaryOfProductRevenueReservesIncludedInConsolidatedBalanceSheetsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsAbstract" name="SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsTableTextBlock" name="SummaryOfShareBasedCompensationExpenseAssociatedWithDifferentProgramsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_SwedishOrphanBiovitrumMember" name="SwedishOrphanBiovitrumMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TaxAccountingCorrection" name="TaxAccountingCorrection" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_TaxAdjustmentsAndSettlementsInterest" name="TaxAdjustmentsAndSettlementsInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_TaxBenefitAndCashReceivedFromStockOptionAbstract" name="TaxBenefitAndCashReceivedFromStockOptionAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TecfideraMember" name="TecfideraMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TermOfLease" name="TermOfLease" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Termofcollaborationagreement" name="Termofcollaborationagreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ThirdPartyAntiCdTwentyMember" name="ThirdPartyAntiCdTwentyMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ThreeBillionMember" name="ThreeBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_ThresholdOfGrossSalesOfToBeAchievedInPrecedingTwelveConsecutiveMonthsUnderOptionOne" name="ThresholdOfGrossSalesOfToBeAchievedInPrecedingTwelveConsecutiveMonthsUnderOptionOne" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_ThresholdOfGrossSalesToBeAchievedInAnyTwelveConsecutiveMonthsUnderOptionOne" name="ThresholdOfGrossSalesToBeAchievedInAnyTwelveConsecutiveMonthsUnderOptionOne" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_TimePeriodForPayingRemainingBalanceDue" name="TimePeriodForPayingRemainingBalanceDue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TimeVestedRestrictedStockUnitsActivityTableTextBlock" name="TimeVestedRestrictedStockUnitsActivityTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TimeVestedRestrictedStockUnitsMember" name="TimeVestedRestrictedStockUnitsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_Totaldeferredchargesandprepaidtaxes" name="Totaldeferredchargesandprepaidtaxes" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="biib_TwoBillionMember" name="TwoBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TwoBillionToTwoPointFiveBillionMember" name="TwoBillionToTwoPointFiveBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TwoPointFiveBillionToThreeBillionMember" name="TwoPointFiveBillionToThreeBillionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_TysabriMember" name="TysabriMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_TysabriProductMember" name="TysabriProductMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_UnconsolidatedJointBusiness" name="UnconsolidatedJointBusiness" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="biib_UndesignatedPreferredStockMember" name="UndesignatedPreferredStockMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_UnrealizedGainLossesOnForeignCurrencyDerivativesNetBeforeTax" name="UnrealizedGainLossesOnForeignCurrencyDerivativesNetBeforeTax" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="biib_UpfrontAndMilestonePaymentsMadeToCollaborativePartner" name="UpfrontAndMilestonePaymentsMadeToCollaborativePartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_UpfrontAndMilestonesPaymentsMadeToCollaborativePartner" name="UpfrontAndMilestonesPaymentsMadeToCollaborativePartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="biib_UpfrontAndReimbursementPaymentMadeToCollaborativePartner" name="UpfrontAndReimbursementPaymentMadeToCollaborativePartner" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_ValuationOfGrantedStockUnitsAbstract" name="ValuationOfGrantedStockUnitsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_VentureCapitalInvestments" name="VentureCapitalInvestments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="biib_VentureCapitalInvestmentsAsPercentageOfOurAssets" name="VentureCapitalInvestmentsAsPercentageOfOurAssets" nillable="true" substitutionGroup="xbrli:item" type="us-types:durationStringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="biib_VentureCapitalInvestmentsMember" name="VentureCapitalInvestmentsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="biib_WeightedAveragePeriodToRecognizeCostOfNonvestedAwards" name="WeightedAveragePeriodToRecognizeCostOfNonvestedAwards" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="instant" />
  <xsd:element id="biib_WindfallTaxBenefitsFromVestingOfStockAwardsExercisesOfStockOptionsAndEsppParticipation" name="WindfallTaxBenefitsFromVestingOfStockAwardsExercisesOfStockOptionsAndEsppParticipation" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
</xsd:schema>
