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, including the Moon and Other Celestial Bodies, is a multilateral treaty forming the basis of international space law, negotiated under the auspices of the United Nations. Opened for signature in the United States, the United Kingdom and the Soviet Union on 27 January 1967 and in force from 10 October 1967, it prohibits placing nuclear weapons in space, limits the Moon and other celestial bodies to peaceful purposes, forbids any country from claiming sovereignty over outer space or a celestial body, and declares that space is to be freely explored and used by all nations as the province of all mankind. As of October 2025, 118 countries are parties to it, including every major spacefaring nation.