United states securities and exchange commission

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For additional information on our collaboration 
arrangement with Eisai, please read Note 20, 
Collaborative and Other Relationships, to our 
consolidated financial statements included in this 
report.
Neurimmune Collaboration Agreement
In October 2017 we amended the terms of our 
collaboration and license agreement with 
Neurimmune Subone AG (Neurimmune). Under the 
amended agreement, we made a $150.0 million 
payment to Neurimmune, which is reflected as a 
charge to noncontrolling interests, in exchange for a 
15% reduction in royalty rates payable on products 
developed under the agreement, including on 
potential commercial sales of aducanumab. Our 
royalty rates payable on products developed under the 
agreement, including on potential commercial sales of 
aducanumab, will now range from the high single 
digits to low-teens. 
Under the amended agreement, we also have an 
option that will expire in April 2018 to further reduce 
our royalty rates payable on products developed under 
the agreement, including on potential commercial 
sales of aducanumab, by an additional 5% in 
exchange for a $50.0 million payment to 
Neurimmune.
For additional information on our collaboration 
arrangement with Neurimmune, please read Note 19, 
Investments in Variable Interest Entities, to our 
consolidated financial statements included in this 
report.
BIIB098 License Agreement
In November 2017 we entered into an exclusive 
license and collaboration agreement with Alkermes 
Pharma Ireland Limited, a subsidiary of Alkermes plc 
(Alkermes), for BIIB098 (formerly known as ALKS 
8700), an oral monomethyl fumarate (MMF) prodrug 
in Phase 3 development for the treatment of relapsing 
forms of MS. 
Under this agreement, we received an exclusive, 
worldwide license to develop and commercialize 
BIIB098 and will pay Alkermes a royalty on potential 
worldwide net sales of BIIB098. Beginning in 2018 we 
are responsible for all development expenses related 
to BIIB098. Alkermes will maintain responsibility for 
regulatory interactions with the FDA through the  
potential approval of the New Drug Application (NDA) 
for BIIB098 for the treatment of MS.
For additional information on our collaboration 
arrangement with Alkermes, please read Note 20, 
Collaborative and Other Relationships, to our 
consolidated financial statements included in this 
report.
Ionis Collaboration Agreement
In December 2017 we entered into a new 
collaboration agreement with Ionis Pharmaceuticals 
Inc. (Ionis) to identify new antisense oligonucleotide 
(ASO) drug candidates for the treatment of SMA. 
Under this agreement, we have the option to license 
therapies arising out of this collaboration and will be 
responsible for the development and 
commercialization of these therapies.
For additional information on our new 
collaboration arrangement with Ionis, please read 
Note 20, Collaborative and Other Relationships, to our 
consolidated financial statements included in this 
report.
Management Changes
During 2017 we appointed several new 
executives, each of whom has significant experience 
in the biopharmaceutical industry and is a leader in 
his or her functional area. These appointments 
included:
•  Michel Vounatsos, Chief Executive Officer; 
•  Jeffrey Capello, Executive Vice President and 
Chief Financial Officer; 
•  Ginger Gregory, Executive Vice President and 
Chief Human Resources Officer; and 
•  Chirfi Guindo, Executive Vice President and Head 
of Global Marketing, Market Access and 
Customer Innovation. 
For additional information on these and our other 
executive officers, please read the subsection entitled 
“Our Executive Officers” included in this report.

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5
Product/Pipeline Developments
Core Growth Areas
Multiple Sclerosis and Neuroimmunology
TECFIDERA (dimethyl fumarate)
•  In April 2017 we presented new real-world data evidence supporting TECFIDERA at the 69
th
 annual meeting of 
the American Academy of Neurology (AAN) in Boston, MA.
We presented a comparison of real-world data that supported TECFIDERA’s strong efficacy relative to other oral 
MS therapies, both in newly-treated MS patients and those previously treated with a prior disease modifying 
therapy (DMT). Subgroup analyses of the open-label studies PROTEC and RESPOND assessed TECFIDERA in 
early MS and early switch patients, respectively. Results showed that TECFIDERA significantly reduced the 
annualized relapse rate over one year in the early MS subgroups, including those who switched to TECFIDERA 
from a prior DMT. Additional data presented at the AAN meeting affirmed the well-characterized, long-term safety 
profile of TECFIDERA in patients treated for up to nine years.
TYSABRI (natalizumab)
•  In February 2017 the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines 
Agency (EMA) adopted a positive opinion to update the TYSABRI E.U. label with pediatric information to remove 
the contraindication in pediatrics and to describe the results of the post-marketing meta-analysis of pediatric 
data. The label update entitles us to apply for a six-month extension to the E.U. patent Supplementary 
Protection Certificate.
•  In April 2017 we presented new real-world data from the TYSABRI Observational Program that confirmed the 
efficacy of TYSABRI and demonstrated that early and continued treatment leads to better clinical outcomes. 
These data were presented at the 69
th
 annual meeting of AAN in Boston, MA.
FAMPYRA (prolonged-release fampridine tablets)
•  In May 2017 the European Commission (EC) granted a standard marketing authorization for FAMPYRA for 
walking improvement in people with MS. 
ZINBRYTA (daclizumab)
•  In July 2017 the EMA announced that it had provisionally restricted the use of ZINBRYTA to adult patients with 
highly active relapsing disease despite a full and adequate course of treatment with at least one DMT or with 
rapidly evolving severe relapsing MS who are unsuitable for treatment with other DMTs. These restrictions 
followed the initiation of an EMA review (referred to as an Article 20 Procedure) of ZINBRYTA following the 
report of a case of fatal fulminant liver failure, as well as four cases of serious liver injury.
•  In October 2017, as part of the Article 20 Procedure of ZINBRYTA, the EMA Pharmacovigilance Risk 
Assessment Committee (PRAC) completed its assessment and recommended a further set of restrictions on 
the use of ZINBRYTA by MS patients.
•  In November 2017 the CHMP adopted an opinion, confirming the PRAC's recommendations, for further 
restrictions to minimize the risk of serious liver injury with ZINBRYTA, including restriction of its use to adult 
patients with relapsing forms of MS who have had an inadequate response to at least two DMTs and for whom 
treatment with any other DMT is contraindicated or otherwise unsuitable. In January 2018 the EC adopted a 
final and legally-binding decision, which concluded the Article 20 Procedure, confirming the CHMP opinion. As a 
result of the CHMP's recommendation of these restrictions, we recorded net impairment charges related to 
intangible assets, inventory, property, plant and equipment and prepaid tax assets, totaling approximately 
$190.8 million. Offsetting these amounts was an unrecorded tax benefit related to certain ZINBRYTA related 
assets totaling approximately $93.8 million.
Opicinumab (anti-LINGO-1)
•  In October 2017 we initiated the Phase 2b clinical trial AFFINITY, designed to evaluate opicinumab as an 
investigational add-on therapy in people with relapsing MS. The trial follows the comprehensive review of 
SYNERGY, a Phase 2 trial, which identified a specific population that may be more likely to respond to 
treatment.

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