Investment banking is where you deal with the largest trades. As a result, the level of risk and pressure involved is often higher than in any other area of banking.
Investment banks do not take deposits, instead they facilitate large scale transactions by individuals and companies. These are to facilitate actions such as mergers and acquisitions and trading on wall street. They are the go between for investors and the organization issuing the securities.
The goal of investment banking is to generate greater profit by investing in foreign exchange, bonds and on the stock market. Investment banks will work quite closely with large scale investors such as Private Equity Funds and Hedge Funds, where the best investment bankers will often end up working.