Biogen is a global biopharmaceutical company focused on treatments for neurological, rare, and immunological diseases. Biogen's historical core is multiple sclerosis, where it treats more MS patients than any other company through drugs including VUMERITY, TYSABRI, TECFIDERA, AVONEX, and PLEGRIDY. This MS franchise is in structural decline as biosimilar and generic competition intensifies, and Biogen is relying on newer products to offset the erosion. In rare disease, Biogen sells SPINRAZA for spinal muscular atrophy, SKYCLARYS for Friedreich's ataxia, and QALSODY for SOD1-ALS — each the first-ever approved treatment in its disease. Biogen's most important growth product is LEQEMBI, a disease-modifying Alzheimer's therapy co-commercialized 50/50 with Eisai, which targets amyloid plaques and holds roughly 60-70% share of anti-amyloid prescriptions globally. Biogen also earns royalty and profit-sharing income from Roche's anti-CD20 drugs RITUXAN and OCREVUS, and co-commercializes ZURZUVAE for postpartum depression with Supernus. Biogen sells primarily through its own sales force to healthcare providers, with U.S. distribution through wholesale and specialty channels. Revenue per patient is high across most of Biogen's portfolio, particularly in rare disease, but patient populations are small and require intensive physician education and care pathway development. Biogen also earns contract manufacturing revenue from its biologics facilities in North Carolina and Switzerland.