Unlike commercial banks and retail banks, investment banks do not take deposits. Industrialized countries, including G8 countries, have historically not maintained such a separation.

There are two main lines of business in investment banking. Trading securities for cash or for other securities (i.e., facilitating transactions, market-making), or the promotion of securities (i.e., underwriting, research, etc.) is the "sell side", while dealing with 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.

An investment bank can also be split into private and public functions with a Chinese wall which separates the two to prevent information from crossing. The private areas of the bank deal with private insider information that may not be publicly disclosed, while the public areas such as stock analysis deal with public information.