This Article examines the recent history and implementation of one of the central provisions in U.S. banking law, section 23A of the Federal Reserve Act. Enacted in 1933 in response to one of the perceived causes of the Great Depression, section 23A imposes quantitative limitations on certain extensions of credit and other transactions between a bank and its affiliates that expose a bank to an affiliate’s credit or investment risk, prohibits banks from purchasing low-quality assets from their nonbank affiliates, and imposes strict collateral requirements with respect to extensions of credit to affiliates. The key purpose of these restrictions is twofold: to protect federally insured depository institutions from excessive credit exposure to their affiliates, and to prevent transfer of federal subsidy to nondepository financial institutions. After the enactment of the Gramm-Leach-Bliley Act of 1999, which removed the Glass-Steagall era prohibition on affiliation between commercial banks and investment banks, section 23A effectively became the principal statutory safeguard preventing the depository system from subsidizing potentially risky activities of nonbanking institutions. However, despite its officially endorsed significance, section 23A remains a largely obscure statute that has not attracted much scholarly attention to date.