SEC rulemaking under Chair Gary Gensler has proceeded at an incredible pace. One of the agency’s latest proposals is intended to close gaps in the dealer registration regime. As market structure and trading practices have evolved, certain unregistered firms have, in effect, been performing a traditional dealer’s role by serving as liquidity providers and making markets in securities, and to address that regulatory gap, the SEC has proposed rules with qualitative criteria for determining whether a firm is acting as a dealer and a quantitative test for classifying a firm as a government securities dealer. If adopted, the rules would primarily capture principal trading firms and proprietary trading firms – but they would also capture certain private funds and investment advisers. This article analyzes the key elements of the proposal. See our coverage of other recent SEC rulemaking on beneficial ownership, cyber risk management, Form PF, private funds, security-based swaps and short sales.