The Outer Space Treaty is a multilateral treaty, formally known as 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 forms the foundational basis of international space law. 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. It was created during the Cold War, following the Soviet Union's launch of Sputnik in 1957, to solve the problem of preventing an arms race in space and the potential militarization of the new domain.
The treaty's key mechanism is to ensure that space is used for peaceful purposes and for the benefit of all countries. Article IV is a core provision, prohibiting States Parties from placing nuclear weapons or any other kinds of weapons of mass destruction 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, forbidding the establishment of military bases or the testing of any type of weapons there. Furthermore, the treaty establishes that outer space is not subject to national appropriation by claim of sovereignty. Article VI makes States Parties internationally responsible for all national space activities, including those carried out by non-governmental entities.
The Outer Space Treaty is the first of five core United Nations treaties on space law. It connects to and is elaborated upon by subsequent agreements, such as the Rescue Agreement (1968), the Liability Convention (1972), and the Registration Convention (1975). While the treaty itself has not been replaced or formally amended, its relevance is debated due to the rise of private space companies and issues like space resource utilization, which it does not explicitly regulate. The Artemis Accords (2020), a non-UN agreement, have emerged as a recent attempt to clarify principles for space exploration, including the use of space resources, creating controversy regarding the treaty's interpretation.