The conclusion of the 1963 Moscow Treaty banning nuclear weapon tests in the atmosphere, in outer space and under water is an important milestone in the history of the Cold War. It was preceded by long and complex negotiations between the USSR and the US. Measures to impose a moratorium on tests (August 1958 — August 1961) did not yield signifi cant results either in reducing harmful environmental consequences or in reducing the risk of nuclear conflict. In addition, the issue of at least partial test ban was closely linked to the political contradictions between the superpowers, in particular, regarding the status of Berlin. On 9 September 1961, the negotiations were stopped. In the fall, the USSR conducted a large series of explosions, and advances in weapons development required new tests. Moscow’s decision to withdraw from the moratorium was dictated by the desire to demonstrate to its opponents the readiness for any emergency. In 1962, the events around Cuba led not only to intensified testing by both powers, but also to the acute Cuban Missile Crisis in October, when the danger of using nuclear weapons became quite real. The August 1963 treaty was one of the immediate outcomes of the Cuban Missile Crisis. However, it is also important that the superpowers came to the signing of the Moscow Treaty only after their scientific and technological achievements (including, above all, the results of nuclear tests) had been able to ensure a confident strategic deterrence of each other. The tests of nuclear devices conducted by both powers in 1961 and 1962 allowed them to equip all types of carriers with warheads as part of their planned programs to renew strategic nuclear arsenals. At the same time, the Moscow Treaty created a basis for harmonizing the positions of the US and the USSR with regard to nuclear nonproliferation for many years to come.