A memorandum of understanding (MoU) describes a bilateral or multilateral agreement between two or more parties. It expresses a convergence of will between the parties, indicating an intended common line of action. It is often used in cases where parties either do not imply a legal commitment or in situations where the parties cannot create a legally enforceable agreement. It is a more formal alternative to a gentlemen's agreement.

Whether or not a document constitutes a binding contract depends only on the presence or absence of well-defined legal elements in the text proper of the document (the so-called "four corners"). The required elements are: offer and acceptance, consideration, and the intention to be legally bound (animus contrahendi). In the U.S., the specifics can differ slightly depending on whether the contract is for goods (falls under the Uniform Commercial Code [UCC]) or services (falls under the common law of the state).