A broker-dealer is a person or firm in the business of buying and selling securities for its own account or on behalf of its customers. The term broker-dealer is used in U.S. securities regulation parlance to describe stock brokerages because most of them act as both agents and principals. A brokerage acts as a broker (or agent) when it executes orders on behalf of its clients, whereas it acts as a dealer or principal when it trades for its own account.