United states securities and exchange commission

---

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
Form 10-K
ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the fiscal year ended December 31, 2017
or
TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
Commission file number: 0-19311
BIOGEN INC.
(Exact name of registrant as specified in its charter)
Delaware
33-0112644
(State or other jurisdiction of incorporation or organization)
(I.R.S. Employer Identification No.)
225 Binney Street, Cambridge, Massachusetts 02142
[phone]
(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)
Securities registered pursuant to Section 12(b) of the Act:
Title of Each Class
Name of Each Exchange on Which Registered
Common Stock, $0.0005 par value
The Nasdaq Global Select Market
Securities registered pursuant to Section 12(g) of the Act:
None
Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities 
Act.    Yes          No 
Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the 
Act.    Yes          No 
Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of 
the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was 
required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes         No 
Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if 
any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the 
preceding 12 months (or for such shorter period that the registrant was required to submit and post such 
files):    Yes          No 
Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained 
herein, and will not be contained, to the best of the registrant’s knowledge, in definitive proxy or information statements 
incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    
Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, 
or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer”, “smaller reporting 
company” and "emerging growth company" in Rule 12b-2 of the Exchange Act.
Large accelerated filer 
Accelerated filer   
Non-accelerated filer 
Smaller reporting company 
(Do not check if a smaller reporting company)
Emerging growth company 
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended 
transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) 
of the Exchange Act. 
Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the 
Act).    Yes          No 
The aggregate market value of the registrant’s common stock held by non-affiliates of the registrant (without admitting 
that any person whose shares are not included in such calculation is an affiliate) computed by reference to the price at 
which the common stock was last sold as of the last business day of the registrant’s most recently completed second 
fiscal quarter was $57,220,188,450.
As of January 26, 2018, the registrant had 211,562,686 shares of common stock, $0.0005 par value, outstanding.
DOCUMENTS INCORPORATED BY REFERENCE
Portions of the definitive proxy statement for our 2018 Annual Meeting of Stockholders are incorporated by reference 
into Part III of this report.

---

Table of Contents
BIOGEN INC.
ANNUAL REPORT ON FORM 10-K
For the Year Ended December 31, 2017
TABLE OF CONTENTS
 
 
Page
PART I
Item 1.
Business
Item 1A.
Risk Factors
Item 1B.
Unresolved Staff Comments
Item 2.
Properties
Item 3.
Legal Proceedings
Item 4.
Mine Safety Disclosures
PART II
Item 5.
Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer 
Purchases of Equity Securities
Item 6.
Selected Financial Data
Item 7.
Management’s Discussion and Analysis of Financial Condition and Results of 
Operations
Item 7A.
Quantitative and Qualitative Disclosures About Market Risk
Item 8.
Financial Statements and Supplementary Data
Item 9.
Changes in and Disagreements with Accountants on Accounting and Financial 
Disclosure
Item 9A.
Controls and Procedures
Item 9B.
Other Information
PART III
Item 10.
Directors, Executive Officers and Corporate Governance
Item 11.
Executive Compensation
Item 12.
Security Ownership of Certain Beneficial Owners and Management and Related 
Stockholder Matters
Item 13.
Certain Relationships and Related Transactions, and Director Independence
Item 14.
Principal Accounting Fees and Services
PART IV
Item 15.
Exhibits and Financial Statement Schedules
Item 16.
Form 10-K Summary
Signatures
Consolidated Financial Statements
1
33
46
46
47
47
48
50
53
88
90
90
91
91
92
92
92
92
92
93
93
97
F- 1

---