United states securities and exchange commission

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Key Developments
During 2017 we had a number of key developments affecting our business.
Corporate Matters
2017 Corporate Strategy
In July 2017 we announced an updated strategic 
framework to optimize the value of our MS business 
while investing for the future across our core growth 
areas of MS and neuroimmunology, AD and dementia, 
movement disorders and neuromuscular diseases, 
including SMA and ALS. We also plan to invest in 
emerging growth areas such as pain, ophthalmology, 
neuropsychiatry and acute neurology. 
In order to deliver positive results in the near 
term while investing in the next stages of our growth, 
we will focus on the following strategic priorities:
•  maximizing the resilience of our MS core 
business;
•  accelerating efforts in SMA as a significant new 
growth opportunity;
•  developing and expanding our neuroscience 
portfolio;
•  focusing our capital allocation efforts to drive 
investment for future growth; and
•  creating a leaner and simpler operating model to 
streamline our operations and reallocate 
resources towards prioritized research and 
development and commercial value creation 
opportunities.
In October 2017, in connection with creating a 
leaner and simpler operating model, we approved a 
corporate restructuring program intended to 
streamline our operations and reallocate resources. 
We expect to make total non-recurring operating and 
capital expenditures of up to $170.0 million, primarily 
in 2018, and our goal is to redirect resources of up to 
$400.0 million annually by 2020 to prioritized 
research and development and other value creation 
opportunities.
TECFIDERA Settlement and License Agreement
In January 2017 we entered into a settlement 
and license agreement with Forward Pharma A/S 
(Forward Pharma). Pursuant to this agreement, we 
obtained U.S. and rest of world licenses to Forward 
Pharma’s intellectual property, including Forward 
Pharma’s intellectual property related to TECFIDERA.  
In exchange, we paid Forward Pharma $1.25 billion in 
cash. During the fourth quarter of 2016 we 
recognized a pre-tax charge of $454.8 million and in 
the first quarter of 2017 we recognized intangible 
assets of $795.2 million related to this agreement. 
We have two intellectual property disputes with 
Forward Pharma, one in the U.S. and one in the E.U., 
concerning intellectual property related to TECFIDERA. 
In March 2017 the U.S. intellectual property dispute 
was decided in our favor. Forward Pharma appealed to 
the U.S. Court of Appeals for the Federal Circuit and 
the appeal is pending. We evaluated the recoverability 
of the U.S. asset acquired from Forward Pharma and 
recorded an impairment charge in the first quarter of 
2017 to adjust the carrying value of the acquired U.S. 
asset to fair value reflecting the impact of the 
developments in the U.S. legal dispute. In January 
2018 the European Patent Office (EPO) announced its 
decision revoking Forward Pharma’s European Patent 
No. 2 801 355. Forward Pharma has stated that it 
expects to file an appeal to the Technical Board of 
Appeal of the EPO. Based upon our assessment of 
these rulings, we continue to amortize the remaining 
net book value of the U.S. and rest of world intangible 
assets in our consolidated statements of income 
utilizing an economic consumption model.
For additional information on our settlement and 
license agreement with Forward Pharma and related 
intangible assets, please read Note 7, Intangible 
Assets and Goodwill, to our consolidated financial 
statements included in this report. For additional 
information on these disputes, please read Note 21, 
Litigation, to our consolidated financial statements 
included in this report.
Tax Reform
The Tax Cuts and Jobs Act of 2017 (the 2017 
Tax Act), which was signed into law on December 22, 
2017, has resulted in significant changes to the U.S. 
corporate income tax system. These changes include 
a federal statutory rate reduction from 35% to 21%, 
the elimination or reduction of certain domestic 
deductions and credits and limitations on the 
deductibility of interest expense and executive 
compensation. The 2017 Tax Act also transitions 
international taxation from a worldwide system to a 
modified territorial system and includes base erosion 
prevention measures on non-U.S. earnings, which has 
the effect of subjecting certain earnings of our foreign 
subsidiaries to U.S. taxation as global intangible low-
taxed income (GILTI). These changes are effective 
beginning in 2018.
The 2017 Tax Act also includes a one-time 
mandatory deemed repatriation tax on accumulated 
foreign subsidiaries' previously untaxed foreign 
earnings (the Transition Toll Tax).

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Changes in tax rates and tax laws are accounted 
for in the period of enactment. Therefore, during the 
year ended December 31, 2017, we recorded a 
charge totaling $1,173.6 million related to our current 
estimate of the provisions of the 2017 Tax Act, 
including a $989.6 million expense under the 
Transition Toll Tax. The Transition Toll Tax will be paid 
over an eight-year period, starting in 2018, and will 
not accrue interest.
The 2017 Tax Act will provide us with flexibility in 
deploying our cash resources to advance our 
business interests. We expect that it will have a 
modest positive effect on our income tax rate in 2018 
and a potential incremental benefit thereafter.
Hemophilia Spin-Off
On February 1, 2017, we completed the spin-off 
of our hemophilia business, Bioverativ Inc. 
(Bioverativ), as an independent, publicly traded 
company trading under the symbol "BIVV" on the 
Nasdaq Global Select Market. The spin-off was 
accomplished through the distribution of all the then 
outstanding shares of common stock of Bioverativ to 
Biogen shareholders, who received one share of 
Bioverativ common stock for every two shares of 
Biogen common stock they owned. The separation 
and distribution was structured to be tax-free for 
shareholders for federal income tax purposes. 
Bioverativ assumed all of our rights and obligations 
under our collaboration agreement with Swedish 
Orphan Biovitrum AB (Sobi) and our collaboration and 
license agreement with Sangamo Biosciences Inc. 
(Sangamo).
Our consolidated results of operations and 
financial position included in this report reflect the 
financial results of our hemophilia business for all 
periods through January 31, 2017.
For additional information on the spin-off of our 
hemophilia business, please read Note 3, Hemophilia 
Spin-Off, to our consolidated financial statements 
included in this report.
BIIB093 Acquisition
In May 2017 we completed an asset purchase of 
the Phase 3-ready candidate BIIB093 (intravenous 
glibencamide) (formerly known as CIRARA) from 
Remedy Pharmaceuticals Inc. (Remedy). The target 
indication for BIIB093 is large hemispheric infarction 
(LHI), a severe form of ischemic stroke where brain 
swelling (cerebral edema) often leads to a 
disproportionately large share of stroke-related 
morbidity and mortality. The U.S. Food and Drug 
Administration (FDA) recently granted BIIB093 Orphan 
Drug Designation for severe cerebral edema in 
patients with acute ischemic (AI) stroke. The FDA has 
also granted BIIB093 Fast Track designation.
Under this agreement, we are responsible for the 
future development and commercialization of 
BIIB093. Remedy will share in the cost of 
development for the target indication for BIIB093 in 
LHI stroke.
For additional information on our transaction with 
Remedy, please read Note 2, Acquisitions, to our 
consolidated financial statements included in this 
report.
BIIB092 License Agreement
In June 2017 we completed an exclusive license 
agreement with Bristol-Myers Squibb Company (BMS) 
for BIIB092 (formerly known as BMS-986168), a 
Phase 2-ready experimental medicine with potential in 
AD and PSP. BIIB092 is an antibody targeting tau, the 
protein that forms the deposits, or tangles, in the 
brain associated with AD and other neurodegenerative 
tauopathies such as PSP. 
Under this agreement, we received worldwide 
rights to BIIB092 and are responsible for the full 
development and global commercialization of BIIB092 
in AD and PSP. 
For additional information on our collaboration 
arrangement with BMS, please read Note 20, 
Collaborative and Other Relationships, to our 
consolidated financial statements included in this 
report.
Eisai Collaboration Agreement
In October 2017 we entered into a new 
collaboration agreement with Eisai Co. Ltd. (Eisai) for 
the joint development and commercialization of 
aducanumab, our anti-amyloid beta antibody 
candidate for AD (Aducanumab Collaboration 
Agreement). Under the Aducanumab Collaboration 
Agreement, we will continue to lead the ongoing 
Phase 3 development of aducanumab and will remain 
responsible for 100% of development costs for 
aducanumab until April 2018. Eisai will then 
reimburse us for 15% of aducanumab development 
expenses for the period April 2018 through December 
2018, and 45% thereafter. Upon commercialization, 
both companies will co-promote aducanumab with a 
region-based profit split.
In addition, we and Eisai will continue to jointly 
develop two product candidates for AD, BAN2401, a 
monoclonal antibody that targets amyloid beta 
aggregates, and E2609, a BACE inhibitor. 
We and Eisai will co-promote AVONEX, TYSABRI 
and TECFIDERA in Japan in certain settings and Eisai 
will distribute AVONEX, TYSABRI, TECFIDERA and 
PLEGRIDY in India and other Asia-Pacific markets, 
excluding China.

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