A nuclear-weapon-free zone (NWFZ) is defined by the United Nations as an agreement that a group of states has freely established by treaty or convention that bans the development, manufacturing, control, possession, testing, stationing or transporting of nuclear weapons in a given area, that has mechanisms of verification and control to enforce its obligations, and that is recognized as such by the General Assembly of the United Nations. NWFZs have a similar purpose to, but are distinct from, the Treaty on the Non-Proliferation of Nuclear Weapons to which most countries including five nuclear weapons states are a party. Another term, nuclear-free zone, often means an area that has banned both nuclear power and nuclear weapons, and sometimes nuclear waste and nuclear propulsion, and usually does not mean a UN-acknowledged international treaty.

The NWFZ definition does not count countries or smaller regions that have outlawed nuclear weapons simply by their own law, like Austria with the Atomsperrgesetz in 1999. Similarly the 2+4 Treaty, which led to German reunification, banned nuclear weapons in the new states of Germany (Berlin and former East Germany), but was an agreement only among the six signatory countries, without formal NWFZ mechanisms.