Start I, officially the Strategic Arms Reduction Treaty was a nuclear weapons limitation treaty between the United States and the Soviet Union.

It was signed on July 31, 1991, five months before the collapse of the Soviet Union. The treaty placed limits on the number of various types of vehicles and warheads that could be deployed by either side. It remains in effect, as a treaty between the US and Russia, Belarus, Kazakhstan, and Ukraine. Belarus, Kazakhstan and Ukraine have since totally disarmed.