content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001769608</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <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>Singhal Priya</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>3806</noOfUnitsSold>
        <aggregateMarketValue>480507.50</aggregateMarketValue>
        <noOfUnitsOutstanding>146527832</noOfUnitsOutstanding>
        <approxSaleDate>05/19/2025</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>02/01/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>1250</amountOfSecuritiesAcquired>
        <paymentDate>02/01/2025</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>02/07/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>1535</amountOfSecuritiesAcquired>
        <paymentDate>02/07/2025</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>02/10/2025</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>855</amountOfSecuritiesAcquired>
        <paymentDate>02/10/2025</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>03/31/2025</acquiredDate>
        <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>166</amountOfSecuritiesAcquired>
        <paymentDate>03/31/2025</paymentDate>
        <natureOfPayment>Cash</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>05/19/2025</noticeDate>
        <planAdoptionDates>
          <planAdoptionDate>02/18/2025</planAdoptionDate>
        </planAdoptionDates>
        <signature>/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Priya Singhal</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
metadata_documents: [{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 4523}]
text: 144
  0001769608
  XXXXXXXX
  LIVE
  0000875045
  BIOGEN INC.
  000-19311
  225 BINNEY STREET
  CAMBRIDGE
  MA
  02142
  7814642000
  Singhal Priya
  Officer
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  3806
  480507.50
  146527832
  05/19/2025
  NASDAQ
  Common
  02/01/2025
  Restricted Stock Vesting
  Issuer
  N
  1250
  02/01/2025
  Compensation
  Common
  02/07/2025
  Restricted Stock Vesting
  Issuer
  N
  1535
  02/07/2025
  Compensation
  Common
  02/10/2025
  Restricted Stock Vesting
  Issuer
  N
  855
  02/10/2025
  Compensation
  Common
  03/31/2025
  ESPP Purchase
  Issuer
  N
  166
  03/31/2025
  Cash
  Y
  05/19/2025
  02/18/2025
  /s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Priya Singhal