An underwriter is any party, usually a member of a financial organization, that evaluates and assumes another party’s risk in mortgages, insurance, loans, or investments for a fee, usually in the form of a commission, premium, spread, or interest.

Underwriters try to determine the likelihood that a borrower will pay as promised and that enough collateral is available if there's a default. In the case of insurance, underwriters seek to assess a policyholder's health and other factors and spread the potential risk among as many people as possible.