Investment banking is an institutional-level banking activity provided to large companies, governments, and other entities. It is separate from commercial banking through regulations, although both may be and often are part of the same bank. Investing banking is not open to retail customers, as it does not take in deposits. Instead, it helps with mergers and acquisitions, the raising of capital, taking companies public (i.e., underwriting), and reorganizations. For these activities, investment banks command high fees.
There are two sides to investment banking — buy and sell. The buy side buys securities for mutual funds, pension funds, and more for money management purposes. The sell side creates and promotes securities to the buy side.