BIIB US Equity☆

Held by — the largest Section 13(f) filers reporting a long position in BIIB for 2026-Q1. A LAGGED quarterly snapshot filed up to 45 days after quarter-end; it excludes shorts, options, cash and non-US-listed lines. “% of shares out” uses the reported cover-page share count and is omitted when that denominator is unusable.
In these books — membership is looked up in a small NAMED set of constituent books (listed in that column); a miss means “not in those books”, never “not in any index”. Each book carries the issuer's own as-of, and cadences differ (daily to quarterly).
Congress — members with a disclosed STOCK Act transaction in BIIB, most recent first, from the API's returned window (so the per-member trade counts in the tooltip are counts within that window, not lifetime). Amounts are disclosed RANGES, not exact values, and reports arrive up to 30–45 days late. As disclosed — no causal claim, not investment advice.
Board & blockholder links — other covered companies that share a director or a 10% owner with BIIB, built from SECTION-16 filings (SEC Forms 3/4/5) only. A person who has not filed a Form 3/4/5 at both companies inside the roster window (2015-07-01 → 2026-06-30) does not appear, so an absent link is not evidence of an absent relationship; each end carries its own filing-date span so the overlap is checkable on the linked name's own page. A reporting owner whose name carries a corporate or fund legal form is a designation right, not a person with a board seat, and is tagged as a fund entity rather than counted as a human interlock. 22 links were to symbols outside the covered universe and are not shown — the restriction that keeps closed-end-fund trustee slates out of an operating-company graph.