Outer Space Treaty — treaty that forms the basis of international space law
The Outer Space Treaty established the foundational legal framework for international space law, barring national sovereignty claims and nuclear weapons in space.
Key Facts
- Opened for signature
- 27 January 1967
- Entered into force
- 10 October 1967
- State parties (as of Oct 2025)
- 118 countries
- Signatories (not yet ratified)
- 20 countries
- Nuclear weapons in space
- Prohibited
- Sovereignty over outer space
- Prohibited for all nations
By the Numbers
Location
Cause → Event → Consequence
Cold War competition between the United States and Soviet Union in space raised fears of militarization and unchecked national rivalry beyond Earth. Drawing on the precedent of the Antarctic Treaty (1961), the United Nations facilitated negotiations to prevent conflict and regulate activities in outer space before they could escalate into a new arena of superpower confrontation.
On 27 January 1967, the Outer Space Treaty was opened for signature simultaneously in Washington, London, and Moscow. It prohibited placing nuclear weapons in orbit, restricted the Moon and other celestial bodies to peaceful use, affirmed free exploration by all states, and barred any nation from claiming sovereignty over outer space or celestial bodies.
The treaty entered into force in October 1967 and became the cornerstone of international space law, eventually drawing 118 state parties. It was followed by four supplementary agreements covering astronaut rescue, liability, registration, and lunar activities, and continues to underpin major multilateral space endeavors such as the International Space Station and the Artemis Program.
Political Outcome
Treaty entered into force 10 October 1967; 118 state parties as of October 2025, prohibiting national sovereignty claims, nuclear weapons in space, and military use of celestial bodies.
No binding international legal framework governing activities in outer space
Outer space declared the province of all mankind, with no sovereign claims permitted and nuclear weapons banned