The Outer Space Treaty is a foundational multilateral treaty in international law, formally titled the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies. It was created during the Cold War, following the launch of Sputnik in 1957, to prevent an arms race in space and ensure the exploration of outer space was for peaceful purposes and the benefit of all countries. The treaty was opened for signature on January 27, 1967, in London, Moscow, and Washington, D.C., and entered into force on October 10, 1967.
The treaty, which has 17 articles, works by establishing key principles for state activities in space. Article II prohibits national appropriation of outer space or celestial bodies by claim of sovereignty, use, or occupation. Article IV is a core arms control provision, forbidding States Parties from placing nuclear weapons or any other kinds of weapons of mass destruction (WMD) in orbit around the Earth, installing them on celestial bodies, or stationing them in outer space. It also mandates that the Moon and other celestial bodies be used exclusively for peaceful purposes, prohibiting military bases, weapons testing, or military maneuvers there. Article VI holds states internationally responsible for all national space activities, including those by non-governmental entities, requiring authorization and continuing supervision.
The Outer Space Treaty is the basis for a network of four subsequent United Nations treaties that elaborate on its principles. These include the Rescue Agreement (1968), which expands on Articles V and VIII regarding the return of astronauts and space objects, and the Liability Convention (1972), which expands on Article VII by establishing absolute liability for launching states for damage caused by their space objects. The treaty has not been formally amended since its creation, but its provisions, such as those on space debris and resource utilization, are increasingly debated due to rapid technological advancements and the rise of private space activities.