Outer Space Treaty
| Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies | |
|---|---|
Parties Signatories Non-parties | |
| Signed | 27 January 1967 |
| Location | London, Moscow and Washington, D.C. |
| Effective | 10 October 1967 |
| Condition | 5 ratifications, including the depositary Governments |
| Parties | 118 |
| Depositary | Governments of the United Kingdom of Great Britain and Northern Ireland, the Union of Soviet Socialist Republics and the United States of America |
| Languages | English, French, Russian, Spanish, Chinese and Arabic |
| Full text | |
| Outer Space Treaty of 1967 at Wikisource | |
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The Outer Space Treaty, formally called 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 that forms the basis of international space law.
Negotiated and drafted under the auspices of the United Nations, it was opened for signature in the United States, the United Kingdom, and the Soviet Union on 27 January 1967, entering into force on 10 October 1967. As of October 2025, 118 countries are parties to the treaty—including all major spacefaring nations—and another 20 are signatories.
Key provisions of the treaty include prohibiting nuclear weapons in space; limiting the use of the Moon and all other celestial bodies to peaceful purposes; establishing that space shall be freely explored and used by all nations; and precluding any country from claiming sovereignty over outer space or any celestial body. Although it forbids establishing military bases, testing weapons and conducting military maneuvers on celestial bodies, the treaty does not expressly ban all military activities in space, nor the establishment of military space forces or the placement of conventional weapons in space.
The OST also declares that space is an area for free use and exploration by all and "shall be the province of all mankind". Drawing heavily from the Antarctic Treaty of 1961, the Outer Space Treaty likewise focuses on regulating certain activities and preventing unrestricted competition that were thought might lead to conflict at that time. Consequently, it is largely silent or ambiguous on newly developed space activities such as lunar and asteroid mining.
OST was at the heart of a 'network' of inter-state treaties and strategic power negotiations to achieve the best available conditions for nuclear weapons world security.
OST was the most important link in the chain of international legal arrangements for space from the late 1950s to the mid-1980s. The OST was followed by four additional agreements, with varied levels of accession: the safe return of astronauts who land in a foreign country (1967); liability for damages caused by spacecraft (1972); the registration of space vehicles (1976); and rules for activities on the Moon (1979). As the first and most foundational legal instrument of space law, the Outer Space Treaty and its broader principles of promoting the civil and peaceful use of space continue to underpin multilateral initiatives in space, such as the International Space Station and the Artemis Program.