An agreement by which a party (the guarantor) assumes responsibility for the payment or performance of an obligation or action of another person (the primary obligor) if that other person defaults. A guarantee creates a secondary obligation to support the primary obligor's primary obligation to a third party. The beneficiary of the guarantee will only have an action against the guarantor if there has been a default by the primary obligor.

In New Zealand, a contract of guarantee must be in writing and signed by the guarantor (section 27, Property Law Act 2007).