3 Historically restricted in common law jurisdictions but generally accepted elsewhere; availability varies between contemporary common law jurisdictions
A collateral contract is usually a single term contract, made in consideration of the party for whose benefit the contract operates agreeing to enter into the principal or main contract, which sets out additional terms relating to the same subject matter as the main contract.[1] For example, a collateral contract is formed when one party pays the other party a certain sum for entry into another contract. A collateral contract may be between one of the parties and a third party.
It can also be epitomized as follows: a collateral contract is one that induces a person to enter into a separate "primary" contract. For example, if X agrees to buy goods from Y that will, accordingly, be manufactured by Z, and does so on the strength of Z's assurance as to the high quality of the goods, X and Z may be held to have made a collateral contract consisting of Z's promise of quality given in consideration of X's promise to enter into the main contract with Y.