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the anticipated amount, timing and accounting of revenues, contingent payments, milestone, royalty and other payments under licensing, collaboration or acquisition agreements, tax positions and contingencies, collectability of receivables, pre-approval inventory, cost of sales, research and development costs, compensation and other selling, general and administrative expenses, amortization of intangible assets, foreign currency exchange risk, estimated fair value of assets and liabilities and impairment assessments;

•	expectations, plans and prospects relating to sales, pricing, growth and launch of our marketed and pipeline products;

•	our plans to invest in emerging growth areas such as pain, ophthalmology, neuropsychiatry and acute neurology;

•	the potential impact of increased product competition in the markets in which we compete;

•	patent terms, patent term extensions, patent office actions and expected availability and period of regulatory exclusivity;

•	the costs and timing of potential clinical trials, filings and approvals, and the potential therapeutic scope of the development and commercialization of our and our collaborators’ pipeline products;

•	the drivers for growing our business, including our plans and intent to commit resources relating to business development opportunities and research and development programs;

•	the anticipated benefits and the potential costs and expenses related to our current or future initiatives to streamline our operations and reallocate resources;

•	our manufacturing capacity, use of third-party contract manufacturing organizations and plans and timing relating to the expansion of our manufacturing capabilities, including anticipated investments and activities in new manufacturing facilities;

•	the potential impact on our results of operations and liquidity of the United Kingdom's (U.K.) intent to voluntarily depart from the European Union (E.U.);

•	the impact of the continued uncertainty of the credit and economic conditions in certain countries in Europe and our collection of accounts receivable in such countries;

•	the potential impact of healthcare reform in the United States (U.S.) and measures being taken worldwide designed to reduce healthcare costs to constrain the overall level of government expenditures, including the impact of pricing actions and reduced reimbursement for our products;

•	the timing, outcome and impact of administrative, regulatory, legal and other proceedings related to our patents and other proprietary and intellectual property rights, tax audits, assessments and settlements, pricing matters, sales and promotional practices, product liability and other matters;

•	lease commitments, purchase obligations and the timing and satisfaction of other contractual obligations;

•	our ability to finance our operations and business initiatives and obtain funding for such activities;

•	the anticipated benefits, costs and tax treatment of the spin-off of our hemophilia business; and

•	the impact of new laws, including the Tax Cuts and Jobs Act of 2017, and accounting standards.

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•	“Biogen,” the “company,” “we,” “us” and “our” refer to Biogen Inc. and its consolidated subsidiaries;

•	“RITUXAN” refers to both RITUXAN (the trade name for rituximab in the U.S., Canada and Japan) and MabThera (the trade name for rituximab outside the U.S., Canada and Japan); and

•	"ELOCTATE" refers to both ELOCTATE (the trade name for Antihemophilic Factor (recombinant), Fc Fusion Protein in the U.S., Canada and Japan) and ELOCTA (the trade name for Antihemophilic Factor (recombinant), Fc Fusion Protein in the E.U.).

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•	In April 2017 we presented new real-world data evidence supporting TECFIDERA at the 69th annual meeting of the American Academy of Neurology (AAN) in Boston, MA.

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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 69th annual meeting of AAN in Boston, MA.

•	In May 2017 the European Commission (EC) granted a standard marketing authorization for FAMPYRA for walking improvement in people with MS.

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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.

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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.

•	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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•	In October 2017 we presented data supporting opicinumab as a potential therapy to repair damage to the central nervous system caused by MS. These data were presented at the seventh Joint Meeting of the European Committee for Treatment and Research in MS and Americas Committee for Treatment and Research in MS (ECTRIMS-ACTRIMS).

•	In January 2017 we presented new data from the Phase 3 ENDEAR study of SPINRAZA, which demonstrated a statistically significant reduction in the risk of death or permanent ventilation in SPINRAZA-treated infants with SMA compared to untreated infants. The data were presented at the British Pediatric Neurology Association annual conference in Cambridge, U.K.

•	In April 2017 the CHMP of the EMA adopted a positive opinion recommending the granting of a marketing authorization in the E.U. for SPINRAZA to treat patients with SMA.

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In April 2017 we presented Phase 3 end of study SPINRAZA data from CHERISH, which demonstrated a highly statistically significant and clinically meaningful improvement in motor function in children with later-onset (most likely to develop Type 2 or Type 3) SMA compared to untreated children. The overall findings continued to support the efficacy and favorable safety profile of SPINRAZA across a broad range of individuals with SMA.

•	In June 2017 the EC granted a marketing authorization for SPINRAZA for the treatment of 5q SMA in pediatric and adult patients in the E.U. SPINRAZA is the first approved treatment in the E.U. for SMA. SPINRAZA was reviewed under the EMA’s accelerated assessment program.

•	In June 2017 we presented robust efficacy and safety data from Phase 2 and Phase 3 SPINRAZA studies at the Cure SMA 2017 Annual SMA Conference in Orlando, FL. Data demonstrated motor function improvements in infants on permanent ventilation and no increase in the risk of adverse events in children with scoliosis.

•	In July 2017 the Japanese Ministry of Health, Labor and Welfare approved the use of SPINRAZA for the treatment of infantile SMA.

•	In September 2017 the Japanese Ministry of Health, Labor and Welfare approved the use of SPINRAZA for the treatment of pediatric and adult patients with SMA.

•	In October 2017 we presented new data at the 22nd International Congress of the World Muscle Society demonstrating that earlier initiation of treatment with SPINRAZA may improve motor function outcomes in infants and children with SMA. Results demonstrated the favorable efficacy and safety profile of SPINRAZA.

•	In October 2017 we and Ionis were awarded the 2017 Prix Galien USA Award for Best Biotechnology Product for SPINRAZA.

•	In November 2017 the end of study results from ENDEAR, the Phase 3 study of SPINRAZA, were published in The New England Journal of Medicine.

•	In March 2017 we presented data from research of aducanumab at the 13th International Conference on Alzheimer’s and Parkinson’s Diseases (AD/PD™) in Vienna, Austria.

•	In April 2017 we presented data from a Phase 1b study of aducanumab at the 69th annual meeting of the AAN in Boston, MA. This data was previously presented at the Clinical Trials on Alzheimer’s Disease (CTAD) meeting

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In May 2017 we announced that we had amended the protocol of the Phase 3 trials of aducanumab. ApoE4 carriers that previously would be on a high dose of 6 mg/kg may now be titrated up to 10 mg/kg. This amendment is being reviewed by regulatory bodies and clinical study ethic independent review boards globally and may be implemented on a country by country basis. The change has already been incorporated in the U.S.

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In July 2017 we presented a new post-hoc analysis of the Phase 1b PRIME study of aducanumab at the Alzheimer’s Association International Conference in London, U.K. Data presented included changes in the cognitive and functional subscores of the clinical dementia rating score. Aducanumab slowed decline on both the cognitive and functional assessments compared to placebo, and the results of all subgroups studied were consistent with the overall study population.

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In August 2017 we announced results from a recently conducted analysis of the LTE of our ongoing Phase 1b study of aducanumab. The updated analyses include data from the placebo-controlled period and the LTE for patients treated with aducanumab up to 24 months in the titration cohort and up to 36 months in the fixed-dose cohorts. The results are consistent with previously reported analyses from this ongoing Phase 1b study and support the design of the ongoing Phase 3 studies of aducanumab for early AD.

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In November 2017 we presented new data from the LTE of our ongoing Phase 1b study of aducanumab at the CTAD meeting in Boston, MA. The data included results from patients in the Phase 1b study who were treated with a gradually increased dose of aducanumab for up to 24 months and those who were treated with a fixed dose of 3, 6 or 10 mg/kg aducanumab for up to 36 months. The results are consistent with previously reported analyses from the Phase 1b study and support the design of the ongoing Phase 3 studies of aducanumab for early AD.

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In December 2017 we announced that an Independent Data Monitoring Committee determined that BAN2401 did not meet the criteria for success based on a Bayesian analysis at 12 months as the primary endpoint in an 856-patient Phase 2 clinical study. Following the predefined study protocol, the blinded study will continue and a comprehensive final analysis will be conducted at 18 months seeking to demonstrate clinically significant results. The results of the final analysis are expected to be obtained during the second half of 2018.

•	In January 2017 we initiated a Phase 1 trial of BIIB076, an anti-tau monoclonal antibody, in healthy volunteers and participants with AD.

•	In June 2017 we dosed our first patient in our Phase 2 study of BIIB092 for PSP.

•	In October 2017 our collaboration partner Ionis announced the initiation of a Phase 1/2a clinical study of IONIS-MAPTRx in patients with mild AD. IONIS-MAPTRx is an antisense drug designed to selectively reduce the production of microtubule-associated protein tau (MAPT), or tau protein, in the brain. We have an option to develop and commercialize IONIS-MAPTRx.

•	In March 2017 we presented data from research of BIIB054, our investigational treatment for Parkinson’s disease, at the 13th International Conference on Alzheimer’s and Parkinson’s Diseases (AD/PD™) in Vienna, Austria.

•	In July 2017 we completed enrollment in the Phase 1 study of BIIB054 in both healthy volunteers and patients with early onset Parkinson’s disease.

•	In January 2018 we dosed our first patient in our Phase 2 SPARK study of BIIB054 in Parkinson's disease.

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•	In August 2017 we completed enrollment in the Phase 2b ACTION2 study evaluating the effects of natalizumab versus placebo on clinical measures of functional independence and activities of daily living in acute ischemic stroke patients.

•	In October 2017 we initiated the Phase 2 OPUS study evaluating the efficacy, safety and tolerability of natalizumab in drug-resistant focal epilepsy.

•	In June 2017 we presented real-world evidence from investigator-initiated studies supported by us demonstrating sustained efficacy and safety of, and high acceptance and adherence in patients initiating treatment with, BENEPALI. These data were presented at the Annual European Congress of Rheumatology (EULAR) in Madrid.

•	In June 2017 the CHMP of the EMA issued a positive opinion for IMRALDI, an adalimumab biosimilar candidate referencing HUMIRA.

•	In August 2017 the EC granted a marketing authorization for IMRALDI.

•	In March 2017 the FDA approved OCREVUS, a humanized anti-CD20 monoclonal antibody, for the treatment of relapsing MS (RMS) and primary progressive MS (PPMS).

•	In July 2017 OCREVUS was approved in Australia for the treatment of RMS and PPMS.

•	In September 2017 OCREVUS was approved in Switzerland for the treatment of RMS and PPMS.

•	In January 2018 the EC granted a marketing authorization for OCREVUS for the treatment of RMS and PPMS.

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In March 2017 Roche announced that the FDA’s Oncologic Drugs Advisory Committee voted unanimously that the benefit-risk of rituximab/hyaluronidase for subcutaneous (under the skin) injection was favorable for the treatment of certain blood cancers. This new co-formulation includes the same monoclonal antibody as intravenous RITUXAN and hyaluronidase, a molecule that helps to deliver medicine under the skin.

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In June 2017 the FDA approved RITUXAN HYCELA (rituximab and hyaluronidase human) for subcutaneous injection for the treatment of adults with previously untreated and relapsed or refractory follicular lymphoma, previously untreated diffuse large B-cell lymphoma and CLL. This new treatment includes the same monoclonal antibody as intravenous RITUXAN in combination with hyaluronidase human, an enzyme that helps to deliver rituximab under the skin.

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In November 2017 the FDA approved GAZYVA in combination with chemotherapy, followed by GAZYVA alone in those who responded, for people with previously untreated advanced follicular lymphoma. The approval is based on results from the Phase 3 GALLIUM study, which showed superior progression-free survival for patients who received this GAZYVA-based regimen compared with those who received a RITUXAN-based regimen as an initial therapy.

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•	In October 2017 we reported that BG00011 (STX-100) achieved proof of biology in a Phase 2a study in patients with idiopathic pulmonary fibrosis (IPF), a chronic irreversible and ultimately fatal disease characterized by a progressive decline in lung function. We plan to initiate a Phase 2b study for BG00011 in 2018.

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(1)	In addition to patent protection, certain of our products are entitled to regulatory exclusivity in the U.S. and the E.U. expected until the dates set forth below:

(2)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2024.

(3)	This patent was revoked in a European opposition. This decision is being appealed. The patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2029.

(4)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2028.

(5)	Reflects SPCs granted in most European countries and pediatric extension in some countries.

(6)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2026.

(7)	This patent is subject to granted SPCs in certain European countries, which extended the patent term in those countries to 2026.

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•	safety or efficacy issues;

•	the introduction or greater acceptance of competing products, including lower-priced competing products;

•	constraints and additional pressures on product pricing or price increases, including those resulting from governmental or regulatory requirements, increased competition or changes in, or implementation of, reimbursement policies and practices of payors and other third parties; or

•	adverse legal, administrative, regulatory or legislative developments.

•	our limited marketing experience within the SMA market, which may impact our ability to develop relationships with the associated medical and scientific community;

•	the lack of readiness of healthcare providers to treat patients with SMA;

•	the effectiveness of our commercial strategy for marketing SPINRAZA; and

•	our ability to maintain a positive reputation among patients, healthcare providers and others in the SMA community, which may be impacted by pricing and reimbursement decisions relating to SPINRAZA.

•	the introduction of more efficacious, safer, less expensive or more convenient alternatives to our MS products, including our own products and products of our collaborators;

•	the introduction of lower-cost biosimilars, follow-on products or generic versions of branded MS products sold by our competitors, and the possibility of future competition from generic versions or prodrugs of existing therapeutics or from off-label use by physicians of therapies indicated for other conditions to treat MS patients;

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•	patient dynamics, including the size of the patient population and our ability to attract new patients to our therapies;

•	damage to physician and patient confidence in any of our MS products or to our sales and reputation as a result of label changes or adverse experiences or events that may occur with patients treated with our MS products;

•	inability to obtain appropriate pricing and reimbursement for our MS products compared to our competitors in key international markets; or

•	our ability to obtain and maintain patent, data or market exclusivity for our MS products.

•	changes in, and implementation of, federal, state or foreign government regulations or private third-party payors’ reimbursement policies;

•	pressure by employers on private health insurance plans to reduce costs;

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consolidation and increasing assertiveness of payors, including managed care organizations, health insurers, pharmacy benefit managers, government health administration authorities, private health insurers and other organizations, seeking price discounts or rebates in connection with the placement of our products on their formularies and, in some cases, the imposition of restrictions on access or coverage of particular drugs or pricing determined based on perceived value; and

•	our value-based contracting pilot program pursuant to which we aim to tie the pricing of our products to their clinical values by either aligning price to patient outcomes or adjusting price for patients who discontinue therapy for any reason, including efficacy or tolerability concerns.

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Risk of Product Loss. The manufacturing process for our products is extremely susceptible to product loss due to contamination, oxidation, equipment failure or improper installation or operation of equipment or vendor or operator error. Even minor deviations from normal manufacturing processes could result in reduced production yields, product defects and other supply disruptions. If microbial, viral or other contaminations are discovered in our products or manufacturing facilities, we may need to close our manufacturing facilities for an extended period of time to investigate and remediate the contaminant.

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Risks of Reliance on Third Parties and Single Source Providers. We rely on third-party suppliers and manufacturers for many aspects of our manufacturing process for our products and product candidates. In some cases, due to the unique manner in which our products are manufactured, we rely on single source providers of raw materials and manufacturing supplies. These third parties are independent entities subject to their own unique operational and financial risks that are outside of our control. These third parties may not perform their obligations in a timely and cost-effective manner or in compliance with applicable regulations, and they may be unable or unwilling to increase production capacity commensurate with demand for our existing or future products. Finding alternative providers could take a significant amount of time and involve significant expense due to the specialized nature of the services and the need to obtain regulatory approval of any significant changes to our suppliers or manufacturing methods. We cannot be certain that we could reach agreement with alternative providers or that the FDA or other regulatory authorities would approve our use of such alternatives.

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Global Bulk Supply Risks. We rely on our principal manufacturing facilities for the production of drug substance for our large molecule products and product candidates. Our global bulk supply of these products and product candidates depends on the uninterrupted and efficient operation of these facilities, which could be adversely affected by equipment failures, labor shortages, natural disasters, power failures and numerous other factors.

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Risks Relating to Compliance with cGMP. We and our third-party providers are generally required to maintain compliance with cGMP and other stringent requirements and are subject to inspections by the FDA and comparable agencies in other jurisdictions to confirm such compliance. Any delay, interruption or other issues that arise in the manufacture, fill-finish, packaging or storage of our products as a result of a failure of our facilities or the facilities or operations of third parties to pass any regulatory agency inspection could significantly impair our ability to develop and commercialize our products. Significant noncompliance could also result in the imposition of monetary penalties or other civil or criminal sanctions and damage our reputation.

•	we may be unable to control the resources our collaborators or third parties devote to our programs or products;

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disputes may arise under the agreement, including with respect to the achievement and payment of milestones or ownership of rights to technology developed with our collaborators or other third parties, and the underlying contract with our collaborators or other third parties may fail to provide significant protection or may fail to be effectively enforced if the collaborators or third parties fail to perform;

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•	the interests of our collaborators or third parties may not always be aligned with our interests, and such parties may not pursue regulatory approvals or market a product in the same manner or to the same extent that we would, which could adversely affect our revenues;

•	third-party relationships and collaborations often require the parties to cooperate, and failure to do so effectively could adversely affect product sales, or the clinical development or regulatory approvals of products under joint control or could result in termination of the research, development or commercialization of product candidates or result in litigation or arbitration; and

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any failure on the part of our collaborators or other third parties to comply with applicable laws and regulatory requirements in the marketing, sale and maintenance of the marketing authorization of our products or to fulfill any responsibilities our collaborators or other third parties may have to protect and enforce any intellectual property rights underlying our products could have an adverse effect on our revenues as well as involve us in possible legal proceedings.

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new laws, regulations or judicial decisions, or new interpretations of existing laws, regulations or judicial decisions, related to health care availability, pricing or marketing practices, compliance with wage and hour laws and other employment practices, method of delivery, payment for health care products and services, compliance with health information and data privacy and security laws and regulations, tracking and reporting payments and other transfers of value made to physicians and teaching hospitals, extensive anti-bribery and anti-corruption prohibitions, product serialization and labeling requirements and used product take-back requirements;

•	changes in the FDA and foreign regulatory approval processes that may delay or prevent the approval of new products and result in lost market opportunity;

•	the hiring freeze implemented by the federal government in 2017, including at the FDA, could impact the review and potential approval of new products, which may adversely affect our business and financial condition;

•	requirements that provide for increased transparency of clinical trial results and quality data, such as the EMA’s clinical transparency policy, which could impact our ability to protect trade secrets and competitively-sensitive information contained in approval applications or could be misinterpreted leading to reputational damage, misperception or legal action which could harm our business; and

•	changes in FDA and foreign regulations that may require additional safety monitoring, labeling changes, restrictions on product distribution or use, or other measures after the introduction of our products to market, which could increase our costs of doing business, adversely affect the future permitted uses of approved products or otherwise adversely affect the market for our products.

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•	the inability to obtain necessary foreign regulatory or pricing approvals of products in a timely manner;

•	uncertainties regarding the collectability of accounts receivable;

•	fluctuations in foreign currency exchange rates that may adversely impact our revenues and net income;

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•	difficulties in staffing and managing international operations;

•	the imposition of governmental controls;

•	less favorable intellectual property or other applicable laws;

•	increasingly complex standards for complying with foreign laws and regulations that may differ substantially from country to country and may conflict with corresponding U.S. laws and regulations;

•	the far-reaching anti-bribery and anti-corruption legislation in the U.K., including the Bribery Act, and elsewhere and escalation of investigations and prosecutions pursuant to such laws;

•	the effects of the implementation of the U.K.’s decision to voluntarily depart from the E.U., known as Brexit;

•	compliance with complex import and export control laws;

•	restrictions on direct investments by foreign entities and trade restrictions;

•	greater political or economic instability; and

•	changes in tax laws and tariffs.

•	the cost of restructurings or other initiatives to streamline our operations and reallocate resources;

•	impairments with respect to investments, fixed assets and long-lived assets, including in-process R&D and other intangible assets;

•	inventory write-downs for failed quality specifications, charges for excess or obsolete inventory and charges for inventory write downs relating to product suspensions, expirations or recalls;

•	changes in the fair value of contingent consideration;

•	bad debt expenses and increased bad debt reserves;

•	outcomes of litigation and other legal or administrative proceedings, regulatory matters and tax matters;

•	milestone payments under license and collaboration agreements; and

•	payments in connection with acquisitions and other business development activities.

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•	Reliance on Third Parties. We are dependent on the efforts of Samsung Bioepis and other third parties over whom we have limited or no control in the development and manufacturing of biosimilars products. If Samsung Bioepis or such other third parties fail to perform successfully, we may not realize the anticipated benefits of our investment in Samsung Bioepis;

•	Regulatory Compliance. Biosimilar products may face regulatory hurdles or delays due to the evolving and uncertain regulatory and commercial pathway of biosimilars products in certain jurisdictions;

•	Intellectual Property and Regulatory Challenges. Biosimilar products may face extensive patent clearances, patent infringement litigation, injunctions or regulatory challenges, which could prevent the commercial launch of a product or delay it for many years;

•	Failure to Gain Market and Patient Acceptance. Market success of biosimilar products will be adversely affected if patients, physicians and/or payors do not accept biosimilar products as safe and efficacious products offering a more competitive price or other benefit over existing therapies;

•	Ability to Provide Adequate Supply. Manufacturing biosimilars is complex. If we encounter any manufacturing or supply chain difficulties, we may be unable to meet higher than anticipated demand; and

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Competitive Challenges. Biosimilar products face significant competition, including from innovator products and from biosimilar products offered by other companies. In some jurisdictions, local tendering processes may restrict biosimilar products from being marketed and sold in those jurisdictions. The number of competitors in a jurisdiction, the timing of approval and the ability to market biosimilar products successfully in a timely and cost-effective matter are additional factors that may impact our success and/or the success of Samsung Bioepis in this business area.

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•	increase our vulnerability to general adverse economic and industry conditions;

•	limit our ability to access capital markets and incur additional debt in the future;

•	require us to dedicate a substantial portion of our cash flow from operations to payments on our indebtedness, thereby reducing the availability of our cash flow for other purposes, including business development efforts, research and development and mergers and acquisitions; and

•	limit our flexibility in planning for, or reacting to, changes in our business and the industry in which we operate, thereby placing us at a competitive disadvantage compared to our competitors that have less debt.

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•	800,000 square feet in Cambridge, MA, which is comprised of offices for our corporate headquarters, and other administrative and development functions and laboratories, of which 242,000 square feet is subleased by multiple companies for general office space, laboratories and manufacturing facilities; and

•	357,000 square feet of office space in Weston, MA, of which 174,000 square feet has been subleased through the remaining term of our lease agreement.

•	357,000 square feet of laboratory and office space;

•	188,000 square feet related to an oral solid dose manufacturing facility;

•	175,000 square feet related to a large-scale biologics manufacturing facility;

•	105,000 square feet related to a small-scale biologics manufacturing facility;

•	84,000 square feet of warehouse space and utilities;

•	70,000 square feet related to a parenteral fill-finish facility; and

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•	43,000 square feet related to a large-scale purification facility.

•	139,000 square feet of warehouse, utilities and support space;

•	70,000 square feet related to a label and packaging facility;

•	50,000 square feet related to a laboratory facility; and

•	47,000 square feet of administrative space.

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(1)

On February 1, 2017, we completed the spin-off of our hemophilia business, Bioverativ, as an independent, publicly traded company. Our consolidated results of operations and financial position 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.

(2)	Product revenues, net reflect the impact of the following product launches:

•	Commercial sales of SPINRAZA in the U.S. began in the fourth quarter of 2016 and in rest of world markets in the first quarter of 2017.

•	Under our collaboration agreement with AbbVie, we began to recognize revenues on sales of ZINBRYTA to third parties in the E.U. in the third quarter of 2016.

•	Under our commercial agreement with Samsung Bioepis, we began to recognize revenues on sales of BENEPALI and FLIXABI to third parties in the E.U. in the first quarter of 2016 and third quarter of 2016, respectively.

•	Commercial sales of ALPROLIX commenced in the second quarter of 2014 and commercial sales of ELOCTATE and PLEGRIDY commenced in the third quarter of 2014.

•	Commercial sales of TECFIDERA began in April 2013.

(3)	Notes payable and other financing arrangements reflects:

•	Our 2017 repayment of our 6.875% notes that were issued in 2008 with an aggregate principal amount of $550.0 million, and

•	The issuance of our senior unsecured notes for an aggregate principal amount of $6.0 billion in September 2015.

(4)	Total Biogen Inc. shareholders' equity reflects the repurchase of approximately 29.9 million shares of our common stock at a cost of approximately $8.7 billion between 2013 and 2017:

•	During 2017 we repurchased and retired approximately 3.7 million shares of our common stock at a cost of $1.0 billion under our 2016 Share Repurchase Program.

•	During 2017 we repurchased approximately 1.2 million shares of our common stock at a cost of $365.4 million under our 2011 Share Repurchase Program.

•	During 2016 we repurchased and retired approximately 3.3 million shares of our common stock at a cost of $1.0 billion under our 2016 Share Repurchase Program.

•	During 2015 we repurchased and retired approximately 16.8 million shares of our common stock at a cost of $5.0 billion under a program authorized by our Board of Directors in May 2015 for the repurchase of up to $5.0 billion of our common stock (2015 Share Repurchase Program).

•	During 2014 and 2013 we repurchased approximately 2.9 million and 2.0 million shares, respectively, of our common stock at a cost of approximately $1.3 billion under our 2011 Share Repurchase Program.

(a)	Total cost and expenses for the year ended December 31, 2017, includes a pre-tax charge to acquired in-process research and development of $120.0 million for an upfront payment made to Remedy upon closing of our asset purchase transaction for BIIB093.

(b)	Net income (loss) attributable to noncontrolling interests, net of tax for the year ended December 31, 2017, includes a pre-tax charge of $150.0 million for a payment to Neurimmune in exchange for a 15% reduction in royalty rates payable on products developed under the agreement, including on potential commercial sales of aducanumab.

(c)	Total cost and expenses for the year ended December 31, 2016, includes a pre-tax charge of $454.8 million related to our January 2017 settlement and license agreement with Forward Pharma.

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(d)	Income tax expense for the year ended December 31, 2017, includes $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. For additional information on the 2017 Tax Act, please read Note 17, Income Taxes, to our consolidated financial statements included in this report.

(e)

Total cost and expenses for the years ended December 31, 2017, 2016 and 2015, include restructuring charges of $0.9 million, $33.1 million and $93.4 million, respectively. In addition, total cost and expenses for the year ended December 31, 2016, also include charges to cost of sales totaling $52.4 million of expenses incurred as a result of our determination to cease manufacturing and vacate our small-scale biologics facility in Cambridge, MA as well as close and vacate our warehouse in Somerville, MA. Total cost and expenses for the years ended December 31, 2017 and 2016, also includes $19.2 million and $18.1 million, respectively, of costs incurred directly related to the spin-off of our hemophilia business into an independent, publicly traded company.

(f)	Net income attributable to Biogen Inc. for the year ended December 31, 2015, includes a pre-tax charge to noncontrolling interest of $60.0 million for a milestone payment due to Neurimmune upon the enrollment of the first patient in a Phase 3 trial for aducanumab.

(g)	Commencing in the second quarter of 2013 product and total revenues include 100% of net revenues related to sales of TYSABRI as a result of our acquisition of all remaining rights to TYSABRI from Elan Pharma International, Ltd (Elan), an affiliate of Elan Corporation, plc. Upon closing of this transaction, our collaboration agreement was terminated.

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Medicaid rebates relate to our estimated obligations to states under established reimbursement arrangements. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in other current liabilities. Our liability for Medicaid rebates consists of estimates for claims that a state will make for the current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, invoices received for claims from the prior quarters that have not been paid, and an estimate of potential claims that will be made for inventory that exists in the distribution channel at period end.

•	Governmental rebates or chargebacks, including VA and PHS discounts, represent our estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices we charge to wholesalers which provide those products. The wholesaler charges us for the

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Managed care rebates represent our estimated obligations to third parties, primarily pharmacy benefit managers. Rebate accruals are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expenses and other current liabilities. These rebates result from performance-based goals, formulary position and price increase limit allowances (price protection). The calculation of the accrual for these rebates is based on an estimate of the customer’s buying patterns and the resulting applicable contractual rebate rate(s) to be earned over a contractual period.

•	Copay assistance represents financial assistance to qualified patients, assisting them with prescription drug co-payments required by insurance. The calculation of the accrual for copay is based on an estimate of claims and the cost per claim that we expect to receive associated with inventory that exists in the distribution channel at period end.

•	Other governmental rebates, non-US pharmaceutical taxes or applicable allowances primarily relate to mandatory rebates and discounts in international markets where government-sponsored healthcare systems are the primary payors for healthcare.

(i)	our share of pre-tax profits and losses in the United States (U.S.) for RITUXAN and GAZYVA;

(ii)	reimbursement of our selling and development expenses in the U.S. for RITUXAN; and

(iii)	other revenues from anti-CD20 therapeutic programs, which primarily consist of our share of pre-tax co-promotion profits on RITUXAN in Canada and royalty revenues on sales of OCREVUS.

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•	Level 1 — Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access;

•	Level 2 — Fair values are determined by utilizing quoted prices for identical or similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves and foreign currency spot rates; and

•	Level 3 — Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

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•	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.

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•	$1.5 billion aggregate principal amount of 2.90% Senior Notes due September 15, 2020, valued at 99.792% of par;

•	$1.0 billion aggregate principal amount of 3.625% Senior Notes due September 15, 2022, valued at 99.920% of par;

•	$1.75 billion aggregate principal amount of 4.05% Senior Notes due September 15, 2025, valued at 99.764% of par; and

•	$1.75 billion aggregate principal amount of 5.20% Senior Notes due September 15, 2045, valued at 99.294% of par.

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(a)

MSUs granted in 2017 include approximately 9,000 MSUs issued in 2017 based upon the attainment of performance criteria set for 2013, in relation to awards granted in that year. MSUs granted during 2017 also include awards granted in conjunction with our annual awards made in February 2017 and MSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant. MSUs granted in 2017 reflect an adjustment based upon the final performance multiplier in relation to shares granted in 2016, 2015 and 2014.

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(a)

CSPUs granted in 2017 include awards granted in conjunction with our annual awards made in February 2017 and CSPUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant. CSPUs granted in 2017 also include CSPUs issued in 2017 based upon the attainment of performance criteria set for 2016 in relation to shares granted in 2016.

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(a)	PUs granted in 2017 include awards granted in conjunction with our annual awards made in February 2017 and PUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant.

(a)	RSUs granted in 2017 primarily represent RSUs granted in conjunction with our annual awards made in February 2017 and awards made in conjunction with the hiring of new employees. RSUs granted in 2017 also include approximately 11,000 RSUs granted to our Board of Directors.

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(1)	Represents sublease income expected to be received for the vacated manufacturing facility in Cambridge, MA, the vacated portion of our Weston, MA facility and other facilities throughout the world.

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(a)	Net income and net income attributable to Biogen Inc. for the first, second, third and fourth quarters of 2017 include a pre-tax charge of $353.6 million, $29.4 million, $30.4 million and $30.8 million, respectively, related to our U.S. and rest of world licenses to Forward Pharma's intellectual property, including Forward Pharma's intellectual property related to TECFIDERA.

(b)	Net income and net income attributable to Biogen Inc. for the second quarter of 2017 includes a pre-tax charge to research and development expense of $300.0 million for an upfront payment to BMS upon the closing of our agreement to exclusively license BIIB092.

(c)	Net income and net income attributable to Biogen Inc. for the second quarter of 2017 includes a pre-tax charge to acquired in-process research and development of $120.0 million for an upfront payment to Remedy upon closing of the asset purchase transaction.

(d)	Net income and net income attributable to Biogen Inc. for the second quarter of 2017 includes a pre-tax charge to research and development expense of $60.0 million for a developmental milestone that became payable to the former shareholders of iPierian upon dosing of the first patient in the Phase 2 PSP study for BIIB092.

(e)	Net income attributable to Biogen Inc., for the fourth quarter of 2017, includes a pre-tax charge to noncontrolling interest of $150.0 million for a payment to Neurimmune in exchange for a 15% reduction in royalty rates payable on potential commercial sales of aducanumab.

(f)	Net income and net income attributable to Biogen Inc. for the fourth quarter of 2017 includes pre-tax charges to research and development expense of $28.0 million and $50.0 million for an upfront payment and a continuation payment, respectively, to Alkermes.

(g)	Net income and net income attributable to Biogen Inc. for the fourth quarter of 2017 includes a pre-tax charge to research and development expense of $25.0 million for an upfront payment to Ionis upon entering into a new collaboration agreement to identify new antisense-oligonucleotide drug candidates for the treatment of SMA.

(h)	Net income and net income attributable to Biogen Inc. for the fourth quarter of 2017 includes $1,173.6 million related to the provisions of the 2017 Tax Act, including a $989.6 million expense under the Transition Toll Tax.

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(i)

Net income and net income attributable to Biogen Inc. for the second, third and fourth quarters of 2016 includes additional pre-tax depreciation expense totaling $15.8 million, $15.7 million and $14.0 million, respectively, as part of our decision to cease manufacturing and vacate our small-scale biologics manufacturing facility in Cambridge, MA as well as close and vacate our warehouse space in Somerville, MA.

(j)	Net income and net income attributable to Biogen Inc. for the third quarter of 2016 includes a pre-tax charge to research and development expense of $75.0 million for a license fee paid to Ionis as we exercised our option to develop and commercialize SPINRAZA.

(k)	Net income and net income attributable to Biogen Inc. for the fourth quarter of 2016 includes a pre-tax charge to research and development expense of $50.0 million for a milestone payment due to Eisai related to the initiation of a Phase 3 trial for E2609.

(l)	Net income and net income attributable to Biogen Inc. for the fourth quarter of 2016 includes a pre-tax charge of $454.8 million related to our January 2017 settlement and license agreement with Forward Pharma.

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