Outer Space Treaty

The Outer Space Treaty, formally the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, is a multilateral treaty that forms the basis of international space law. Negotiated under the auspices of the United Nations, it was opened for signature in the United States, the United Kingdom, and the Soviet Union on 27 January 1967 and entered into force on 10 October 1967. As of October 2025, 118 countries are party to it, including every major spacefaring nation. Its key provisions prohibit nuclear weapons in space, limit use of the Moon and other celestial bodies to peaceful purposes, establish that space is to be freely explored by all nations, and prevent any country from claiming sovereignty over outer space or a celestial body.