A majority of investment banks offer strategic advisory services for mergers, acquisitions, divestiture or other financial services for clients, such as the trading of derivatives, fixed income, foreign exchange, commodity, and equity securities.

Trading securities for cash or securities (i.e., facilitating transactions, market-making), or the promotion of securities (i.e., underwriting, research, etc.) is referred to as the “sell side.”

Dealing with the pension funds, mutual funds, hedge funds, and the investing public who consume the products and services of the sell-side in order to maximize their return on investment constitutes the “buy side”. Many firms have buy and sell side components.

The largest bulge-bracket firms (by market capitalization) on Wall Street include Goldman Sachs, Merrill Lynch, Morgan Stanley, and Lehman Brothers. Credit Suisse, Citigroup, Deutsche Bank, JP Morgan Chase, and UBS AG are “universal banks” rather than bulge-bracket investment banks, since they also accept deposits (though not all of them have U.S. branches.)