Investment banks help companies and governments raise money and advise on major financial decisions. They underwrite securities, arrange mergers and acquisitions, and provide trading and research services. They do not take deposits from ordinary people. They serve corporations, institutions, and governments. The largest, like Goldman Sachs, Morgan Stanley, and JPMorgan, operate globally.

The core businesses are three. Advisory handles mergers, acquisitions, restructurings, and divestitures. Underwriting raises capital by selling stocks and bonds to investors. Sales and trading buys and sells securities for clients and, in some cases, for the bank's own account. Research supports all three by analyzing companies, industries, and economies.

Investment banking is cyclical. When markets are active, fees are enormous. When they freeze, layoffs follow. The work is demanding. Junior bankers routinely work 80-hour weeks. The pay is high, but so is the attrition. Many use the job as a stepping stone to private equity, hedge funds, or corporate finance.

The 2008 crisis changed the industry. Lehman Brothers failed. Bear Stearns and Merrill Lynch were absorbed. The remaining big banks face stricter capital rules and limits on proprietary trading under the Volcker Rule. The business is still lucrative, but it is more regulated and more cautious than before.