Investment banks, aka i-banks, assist public and private corporations in raising funds in the capital markets (both equity and debt), as well as in providing strategic advisory services for mergers, acquisitions and other types of financial transactions. They also act as intermediaries in trading for clients. Investment banks differ from commercial banks, which take deposits and make commercial and retail loans. In recent years, however, the lines between the two types of structures have blurred, especially as commercial banks have offered more investment banking services. In the US, the Glass-Steagall Act, initially created in the wake of the Stock Market Crash of 1929, prohibited banks from both accepting deposits and underwriting securities; Glass-Steagall was repealed by the Gramm-Leach-Bliley Act in 1998. Investment banks may also differ from brokerages, which in general assist in the purchase and sale of stocks, bonds, and mutual funds. However some firms operate as both brokerages and investment banks; this includes some of the best known financial services firms in the world.

Source: Wikipedia (http://en.wikipedia.org/wiki/Investment_banking)