In which type of contract is one party not required to act until the other performs?

In a unilateral contract, one party makes a promise contingent upon the performance of a specific act by the other party. The key characteristic of this type of contract is that only one party is obligated to perform once the other party fulfills the specified condition or act. For example, if someone offers a reward for the return of a lost pet, the offeror is bound to pay the reward only when the act of returning the pet is completed. This illustrates that the party offering the contract has a duty only after the other party takes action, reinforcing the concept that one party is not obligated until the other party performs.

In contrast, a bilateral contract involves mutual obligations, where both parties commit to perform certain duties. An executory contract refers to agreements in which some portion of the performance is still pending from either party, and an implied contract is formed based on the actions or circumstances rather than explicit verbal or written agreements. These concepts differentiate unilateral contracts by emphasizing that they arise from contingent actions rather than mutual commitments.