What type of contract calls for an act in consideration for a promise?

A unilateral contract is a type of agreement where one party makes a promise in exchange for the act of another party. In this scenario, only one party is bound to fulfill an obligation; the other party is not required to act until they choose to fulfill the conditions of the contract.

For example, if someone offers $100 to anyone who finds and returns their lost dog, the offeror is making a promise, and the seer of the dog only needs to act (find and return the dog) to receive the reward. This exemplifies the nature of a unilateral contract, which is reliant on the performance of an act rather than a mutual exchange of promises.

This contrasts with a bilateral contract, where both parties make reciprocal promises to each other, thereby securing mutual obligations. A void contract is not legally enforceable from the moment it is created, while an implied contract is formed through the actions of the parties rather than a written or spoken agreement. Each of these other types of contracts does not match the criteria of requiring an act in exchange for a promise as clearly as a unilateral contract does.