What treaty banned nuclear weapon tests in the atmosphere, outer space, and underwater in 1963?

The 1963 treaty banning nuclear tests in the atmosphere, outer space and underwater was the Partial Test Ban Treaty.

Formally called the Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, it was signed in Moscow on 5 August 1963 by the United States, the Soviet Union and the United Kingdom. It entered into force on 10 October 1963.

The treaty prohibited nuclear explosions in those environments and also barred explosions that could cause radioactive debris to cross national borders. Underground tests were not banned, because negotiators had not resolved how to verify them without intrusive inspections.

The treaty is also called the Limited Test Ban Treaty. It did not end nuclear testing or nuclear proliferation: France and China, which were not parties, continued atmospheric tests for years, while underground testing continued elsewhere. It is distinct from the later Nuclear Non-Proliferation Treaty and the Comprehensive Nuclear-Test-Ban Treaty.