This document discusses different types of contracts including valid, void, voidable, express, implied, quasi, executed, and executory contracts. A valid contract exists when all essential elements are present. A void contract has no legal effect. A voidable contract allows one party the option to void the contract if consent was not free. An express contract uses spoken or written words while an implied contract uses acts or conduct. A quasi contract arises due to special circumstances rather than agreement. An executed contract means both parties fulfilled obligations while an executory contract means obligations remain.