Underwriting refers to the process that a large financial service provider (bank, insurer, investment house) uses to assess the eligibility of a customer to receive their products (equity capital, insurance, mortgage, or credit). Underwriters exist in a number of different industries, and are primarily responsible for evaluating the risk of potential clients.
In investment banking, underwriters are best known for the role that they play in initial public offerings (IPOs). IPOs are when a company decides to sell equity on the stock market for the first time . They sell their own stock on the market and in the process, raise money through selling equity. However, investment banks are involved in the underwriting of all types of securities, not just stock.
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Firms may issue an IPO on an exchange such as the New York Stock Exchange (NYSE). They sell their stock in exchange for cash.
The company needs to set a price for its stock; they want to set it high enough to raise as much money as possible but low enough that they will be able to sell their stock. Thus, there is a risk to the company in the offering of securities. For all types of securities, whether offered by companies or the government, there is a risk that the issuer may not be able to have a successful securities offering.
That is where the job of the security underwriter comes in. The underwriter offers to take on some of the risk of the offering in exchange for a premium. In essence, the underwriter buys the securities from the issuer and then turns around to sell the securities on the market. This means that the issuer gets cash up front. The issuer knows that it is probably not getting the full market value of the securities, but that's okay because it no longer has the risk of having to find enough buyers to purchase the securities at a desirable price. The underwriting investment bank likes the deal because if it can sell the securities on the market at a higher price than it purchased them, it can make a profit.
There are sometimes multiple investment banks involved in the underwriting of a security. The details of the process may vary from deal to deal, but the fundamental job of the underwriter(s) is to take some of the issuer's risk in exchange for a premium.