Outer Space Treaty

The Outer Space Treaty was spurred by the development of intercontinental ballistic missiles (ICBMs) in the 1950s, which could reach targets through outer space. The United States proposed an inspection program for rockets in August 1957. The Soviet Union instead tested ICBMs and launched Sputnik, the first artificial satellite, in October 1957.

From 1959 to 1962, Western allies proposed various outer space arms control treaties, with US President Dwight Eisenhower proposing an outer space treaty similar to the Antarctic Treaty to the United Nations General Assembly on September 22, 1960. According to the United States Department of State, the Soviet Union did not accept these proposals unless the US removed its overseas missile bases. The Soviet Union de-linked these proposals after the 1963 signing of the Limited Test Ban Treaty.

On 17 October 1963, the U.N. General Assembly unanimously adopted a resolution prohibiting the introduction of weapons of mass destruction in outer space. Various proposals for an arms control treaty governing outer space were debated during a General Assembly session in December 1966. US drafts covered only celestial bodies; it accepted the Soviet version which applied a WMD ban to all of outer space. Adoption of the final Outer Space Treaty was completed in January 1967.

The Outer Space Treaty represents the basic legal framework of international space law. According to the U.N. Office for Outer Space Affairs (UNOOSA), the core principles of the treaty are:

Among its principles, it bars states party to the treaty from placing weapons of mass destruction in Earth orbit, installing them on the Moon or any other celestial body, or otherwise stationing them in outer space. It specifically 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 (Article IV). However, the treaty does not prohibit the placement of conventional weapons in orbit, and thus some highly destructive attack tactics, such as kinetic bombardment, are still potentially allowable. In addition, the treaty explicitly allows the use of military personnel and resources to support peaceful uses of space, mirroring a common practice permitted by the Antarctic Treaty regarding that continent. The treaty also states that the exploration of outer space shall be done to benefit all countries and that space shall be free for exploration and use by all the states.

Article II of the treaty explicitly forbids any government from "appropriating" a celestial body such as the Moon or a planet, whether by declaration, use, occupation, or "any other means". …

The "Declaration of the First Meeting of Equatorial Countries", also known as the "Bogota Declaration", was one of the few attempts to challenge the Outer Space Treaty. It was promulgated in 1976 by eight equatorial countries to assert sovereignty over those portions of the geostationary orbit that continuously lie over the signatory nations' territory. These claims did not receive wider international support or recognition, and were subsequently abandoned. The thinking of the New International Economic Order informs the 1976 Bogota Declaration, but the Declaration was not widely adopted. So orbital space slots remained under the management of the International Telecommunication Union (ITU).

As the first international legal instrument concerning space, the Outer Space Treaty is considered the "cornerstone" of space law. It was also the first major achievement of the United Nations in this area of law, following the adoption of the first U.N. General Assembly resolution on space in 1958, and the first meeting of the U.N. Committee on the Peaceful Uses of Outer Space (COPUOS) the subsequent year.

Within roughly a decade of the treaty's entry into force, several other treaties were brokered by the U.N. to further develop the legal framework for activities in space:

With the exception of the Moon Treaty, to which only 18 nations are party, all other treaties on space law have been ratified by most major space-faring nations (namely those capable of orbital spaceflight). COPUOS coordinates these treaties and other questions of space jurisdiction, aided by the U.N. Office for Outer Space Affairs.

The Outer Space Treaty 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 parties to the treaty, while another 20 have signed the treaty but have not completed ratification.

Multiple dates indicate the different days in which states submitted their signature or deposition, which varied by location: (L) for London, (M) for Moscow, and (W) for Washington, D.C. Also indicated is whether the state became a party by way of signature and subsequent ratification, by accession to the treaty after it had closed for signature, or by succession of states after separation from some other party to the treaty.

The Republic of China (Taiwan), which is currently recognized by 11 UN member states, ratified the treaty prior to the United Nations General Assembly's vote to transfer China's seat to the People's Republic of China (PRC) in 1971. When the PRC subsequently ratified the treaty, they described the Republic of China's (ROC) ratification as "illegal". The ROC has committed itself to continue to adhere to the requirements of the treaty, and the United States has declared that it still considers the ROC to be "bound by its obligations".

20 states have signed but not ratified the treaty.