Institutional ownership disclosures are the SEC's required transparency framework for the largest investors in U.S. equity markets.

Form 13F is the quarterly disclosure required of institutional investment managers exercising investment discretion over $100 million or more in Section 13(f) securities (broadly, U.S.-listed equities and listed equity options).

The form must be filed within 45 days of quarter-end and lists the manager's holdings — name of issuer, number of shares, market value at quarter-end, voting authority, and discretion type. The 45-day lag is a structural limitation but the filings are the canonical record of institutional ownership for the entire U.S.

public equity market. Schedule 13D (filed within 10 days of crossing the 5% beneficial-ownership threshold under Section 13(d)) is the framework for disclosure of activist or material accumulations. Schedule 13G is the alternative for passive investors crossing the 5% threshold without activist intent.