A memorandum of understanding (MOU) is a legal document describing an agreement between parties. It is a more formal alternative to a gentlemen's agreement, but less formal than a contract.

Examples of MOUs include:

• the Oil for Food program, for which Iraq signed an MOU in 1996,
• the 1997 document signed by President Bill Clinton and the Union of Soviet Socialist Republics successor states updating the Anti-Ballistic Missile Treaty, and
• the MOU between Bush and Kerry for 2004 debates.