An underwriter is a securities specialist that buys bonds and stocks when they are first issued, and resells them to the investing public. An underwriter takes on the risk of securities placement from issuers, and profits by marking up the securities prior to their sale to the public. The underwriter also charges a significant fee to the issuer for this service. The distribution of securities may not be an especially risk endeavor for an underwriter, since it usually has a network of buyers already in place, and so can sell securities with a minimal holding period. Underwriters frequently band together in syndicates when an especially large securities offering needs to be sold; doing so spreads the risk and also accesses a larger group of potential buyers.

In the insurance field, an underwriter evaluates insurance proposals to determine the amount of risk associated with them, and sets insurance premiums based on this perceived risk level.