A surety is a person who agrees to be responsible for the debt or obligation of another. The situation in which a surety is most typically required is when the ability of the primary obligor or principal to perform its obligations under a contract is in question, or when there is some public or private interest which requires protection from the consequences of the principal's default or delinquency. In most common law jurisdictions, a contract of suretyship is subject to the statute of frauds (or its equivalent local laws) and is only enforceable if memorialized by a writing signed by the surety.

A surety bond is a contract between at least three parties: (i) the principal, (ii) the obligee, and (iii) the surety. Through this agreement, the surety agrees to make the obligee whole (usually by payment of money) if the principal defaults in its performance of its promise to the obligee. The contract is formed so as to induce the obligee to contract with the principal, i.e., to demonstrate the credibility of the principal.