The Outer Space 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, is a treaty that forms the basis of international space law. The treaty was opened for signature in the United States, the United Kingdom, and the Soviet Union on January 27, 1967, and entered into force on October 10, 1967. As of January 2008, 99 countries are states-parties to the treaty, while another 26 have signed the treaty but have not yet completed ratification.The Outer Space Treaty represents the basic legal framework of international space law. Among its principles, it bars States Parties to the Treaty from placing nuclear weapons or any other weapons of mass destruction in orbit of Earth, installing them on the Moon or any other celestial body, or to otherwise station them in outer space. It exclusively limits the use of the Moon and other celestial bodies to peaceful purposes and expressly prohibits their use for testing weapons of any kind, conducting military maneuvers, or establishing military bases, installations, and fortifications (Art.IV). However, the Treaty does not prohibit the placement of conventional weapons in orbit.

The treaty explicitly forbids any government from claiming a celestial resource such as the Moon or a planet, since they are the Common heritage of mankind.[1] Art. II of the Treaty states, in fact, that "outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means". The pendant for giving up sovereignty in outer space is the jurisdiction and control that the State that launches a space object retains. According to Manfred Lachs, jurisdiction and control is giving the means to the State to conduct a mission of space exploration.