Investment banks, as opposed to commercial 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.

Indeed the original purpose of an investment bank was to raise capital and advise on mergers and acquisitions and other corporate financial strategies. As banking firms have been performing diversified activities, investment banks have come to fill a variety of roles including underwriting and distributing new security issues, offering brokerage services to public & institutional investors, providing financial advice to corporate clients, especially on security issues, providing advices on merger and acquisition deals, providing financial security research to investors and corporate customers etc. Investment banks have also moved into foreign currency exchange, private banking, and bridge financing.

A key role of investment banks is to advise companies in raising money or funds. There are two ways of raising funds that investment bankers typically engage in: raising funds through the capital markets and raising funds through private placements. Investment bankers can raise funds in capital markets in two ways. They can sell the company's equities in the stock market in an initial public offering (IPO) or secondary offering, or they can give advices on debt issues to the companies. Investment bankers also advise companies on private placements, which mean purchase or sale of corporate securities by private companies or individuals. Types of private placement transactions include venture capital investments, strategic investments by companies, private equity investments, private debt placements, acquisitions, divestitures, and merchant banking.

Investment banks possess an extensive network of industry and financial contacts, current market knowledge, legal processes and comparable market events that will make their clients to create an edge to their competitors. Some of the major global public and private investment banks are ABN Amro, Banc of America Securities, Barclays Capital, Bear Stearns, BNP Paribas, Brown Brothers Harriman and Calyon.