Broker-Dealers vs. Investment Advisers
A broker-dealer effects securities transactions — as broker (agent) for customers or dealer (principal) for its own account — and is paid by commissions and markups; an investment adviser is paid fees for giving investment advice.
Many firms are dually registered as both. Other market participants the SIE names include institutional investors (mutual funds, pensions, insurers), retail investors, custodians that hold customer assets, transfer agents that maintain shareholder records, and depositories like the DTCC.