A treaty governing what states may do in outer space came into force on October 10, 1967, nine months after the United States, the Soviet Union and Britain opened it for signature. Its central rule is that no country may own any part of space: the Moon and other celestial bodies are named in the text, which says outright that they are not open to national appropriation by claim of sovereignty, by use, by occupation or by any other means, and that weapons of mass destruction may not be placed in orbit around the earth or on them.
It was written quickly. The alternative was worse. It was coming. Sputnik had gone up a decade before, both superpowers were flying reconnaissance satellites, the United States had studied a military base on the Moon under a programme called Project Horizon, and the Soviet Union had put a man in orbit. Nobody wanted a claim staked by whoever got there first. The treaty that came out is short, seventeen articles, and it is the foundation of what is now called space law, in the sense that everything else in the field has been built on top of it.
Three of its rules are the ones that still matter. Space is free for exploration and use by all states, which is what makes satellite overflight legal. The Moon and other bodies are to be used for peaceful purposes only, and military manoeuvres and weapons testing are banned there. And each state is responsible for what its own agencies and its own companies do off the earth, and is liable for the damage, which is why launch licences exist at all and why a private rocket is supervised by the country it flies from.
More than 100 states have ratified it and the wording has never been amended. Later agreements added detail: a rescue agreement in 1968, a liability convention in 1972, a registration convention in 1975, and a Moon agreement in 1979 that almost nobody signed, largely over the same argument about resources. Mining on the Moon and on asteroids is the open question now, and the text was not written for it.