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        <filerCredentials>
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          <ccc>XXXXXXXX</ccc>
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      <liveTestFlag>LIVE</liveTestFlag>



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      <issuerCik>0000875045</issuerCik>
      <issuerName>BIOGEN INC.</issuerName>
      <secFileNumber>000-19311</secFileNumber>
      <issuerAddress>
        <com:street1>225 BINNEY STREET</com:street1>
        <com:city>CAMBRIDGE</com:city>
        <com:stateOrCountry>MA</com:stateOrCountry>
        <com:zipCode>02142</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>7814642000</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Gregory Ginger</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Officer</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Fidelity Brokerage Services LLC</name>
        <address>
          <com:street1>900 Salem Street</com:street1>
          <com:city>Smithfield</com:city>
          <com:stateOrCountry>RI</com:stateOrCountry>
          <com:zipCode>02917</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>2681</noOfUnitsSold>
      <aggregateMarketValue>804300.00</aggregateMarketValue>
      <noOfUnitsOutstanding>144742305</noOfUnitsOutstanding>
      <approxSaleDate>04/28/2023</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>02/10/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>755</amountOfSecuritiesAcquired>
      <paymentDate>02/10/2023</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>02/12/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>1463</amountOfSecuritiesAcquired>
      <paymentDate>02/12/2023</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>02/18/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>463</amountOfSecuritiesAcquired>
      <paymentDate>02/18/2023</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <noticeSignature>
      <noticeDate>04/28/2023</noticeDate>
      <planAdoptionDates>
        <planAdoptionDate>02/22/2023</planAdoptionDate>
      </planAdoptionDates>
      <signature>/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Ginger Gregory</signature>
    </noticeSignature>
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144
0001545716
XXXXXXXX
LIVE
0000875045
BIOGEN INC.
000-19311
225 BINNEY STREET
CAMBRIDGE
MA
02142
7814642000
Gregory Ginger
Officer
Common
Fidelity Brokerage Services LLC
900 Salem Street
Smithfield
RI
02917
2681
804300.00
144742305
04/28/2023
NASDAQ
Common
02/10/2023
Restricted Stock Vesting
Issuer
N
755
02/10/2023
Compensation
Common
02/12/2023
Restricted Stock Vesting
Issuer
N
1463
02/12/2023
Compensation
Common
02/18/2023
Restricted Stock Vesting
Issuer
N
463
02/18/2023
Compensation
Y
04/28/2023
02/22/2023
/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Ginger Gregory