United States securities and exchange commission logo June 17, 2021 Michael McDonnell Executive Vice President and Chief Financial Officer BIOGEN INC. 225 Binney Street Cambridge, MA 02142 Re: BIOGEN INC. Form 10-K for Fiscal Year Ended December 31, 2020 Filed February 3, 2021 Form 8-K Filed February 3, 2021 Response dated June 9, 2021 File No. 000-19311 Dear Mr. McDonnell: We have reviewed your June 9, 2021 response to our comment letter and have the following comment. Please respond to this comment within ten business days by providing the requested information or advise us as soon as possible when you will respond. After reviewing your response to this comment, we may have additional comments. Form 8-K Filed February 3, 2021 Exhibit 99.1, page 1 1. We appreciate the additional information provided to us. We continue to believe that your adjustments to exclude from R&D expense and net income attributable to Biogen, Inc. the upfront and premium payments made for collaboration agreements are inconsistent with the guidance in Question 100.01 of the Non-GAAP Financial Measures Compliance and Disclosure Interpretations. Please confirm to us that you will no longer include these adjustments in any non-GAAP financial measure presented in accordance with Item 10(e) of Regulation S-K or Regulation G for all periods presented in future filings. Michael McDonnell BIOGEN INC. June 17, 2021 Page 2 You may contact Tracey Houser at 202-551-3736 or Jeanne Baker at 202-551-3691, if you have questions regarding comments on the financial statements and related matters. FirstName LastNameMichael McDonnell Sincerely, Comapany NameBIOGEN INC. Division of Corporation Finance June 17, 2021 Page 2 Office of Life Sciences FirstName LastName