The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies — mercifully shortened to the Outer Space Treaty (OST), 1967 — was signed on 27 January 1967 and entered into force on 10 October 1967.
It was negotiated at the United Nations at the height of the Cold War, when the US and USSR agreed on very little. That they could agree on this shows how seriously both sides feared an unregulated space race.
The Core Principles — In Simple Language
The Treaty rests on a few foundational ideas, each of which continues to shape space law today.
First — No sovereignty in outer space. Article II is the philosophical heart of the treaty. Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by use, by occupation, or by any other means. In simple language — no country can plant a flag on the Moon and say "this is mine." No matter how many astronauts you land, no matter how much of the surface you explore, the Moon does not become your territory. The 1969 US flag on the Moon is a symbol, not a claim.
Second — Space is the province of all mankind. Article I says the exploration and use of outer space shall be carried out for the benefit and in the interests of all countries, irrespective of their level of economic or scientific development. This means space is not just for the rich and powerful — even countries without space programmes have a stake in how it is used.
Third — Peaceful use only, no weapons of mass destruction in orbit. Article IV bans placing nuclear weapons or any other weapons of mass destruction in orbit, on the Moon, or on any celestial body. Military bases, weapons testing, and military manoeuvres on the Moon are prohibited. Importantly, the treaty does not prohibit conventional military satellites — reconnaissance and communication satellites for defence purposes are allowed. This grey area is a source of ongoing debate.
Fourth — States are responsible for their private actors. Article VI is crucial in today's era of private space companies like SpaceX and Blue Origin. It says states are internationally responsible for national activities in outer space, whether carried out by governmental agencies or by non-governmental entities. If SpaceX causes damage to another country's satellite, the United States government is legally responsible — not just the company. This is a departure from usual international law, where states are usually not held liable for private actions.
Fifth — Liability for damage. Article VII lays down that a launching state is internationally liable for damage caused by its space objects. This principle was later fleshed out into a separate treaty in 1972.
Sixth — Astronauts as envoys of mankind. Article V treats astronauts as envoys of mankind — meaning, if an astronaut of one country is in distress or lands in another country's territory, that country has a duty to help and return them safely.
The Big Picture
The Outer Space Treaty is often called the Magna Carta of space law. It laid down the principles that all subsequent treaties would elaborate. It is signed and ratified by more than 110 countries, including all major spacefaring nations — the US, Russia, China, India, France, UK, and Japan.
But like any old constitution, it has limits. It was written when only two countries could launch anything, before commercial space, before Moon mining, before mega-constellations of satellites like Starlink. The core principles still hold, but modern activities keep raising questions the drafters never imagined.