In August of 1945, when the United States dropped two atomic bombs on Japan, World War II came to a conclusion.

Continued testing of atomic and then hydrogen devices lead to a rising concern about the effects of radioactive fallout. As knowledge of the nature and effects of fallout increased, and as it became apparent that no region in the world was untouched by radioactive debris, the issue of continued nuclear tests drew widened and intensified public attention. Apprehension was expressed about the possibility of a cumulative contamination of the environment and of resultant genetic damage.

Efforts to negotiate an international agreement to end nuclear tests began in the Subcommittee of Five (the United States, the United Kingdom, Canada, France, and the Soviet Union) of the United Nations Disarmament Commission in May 1955. Public interest in the course of the negotiations was active and persistent. A dozen resolutions of the UN General Assembly addressed the issue, repeatedly urging conclusion of an agreement to ban tests under a system of international controls. Efforts to achieve a test ban agreement extended over eight years because they involved complex technical problems of verification and the difficulties of reconciling deep-seated differences in approach to arms control and security. The uneven progress of the negotiations was also a result of regular fluctuations in East-West political relationships during the Cold War.

The Test Ban Treaty was signed in Moscow on August 5, 1963; ratified by the United States Senate on September 24, 1963; and entered into force on October 10, 1963. The treaty prohibited nuclear weapons tests "or any other nuclear explosion" in the atmosphere, in outer space, and under water. While not banning tests underground, the treaty prohibited such explosions if they caused "radioactive debris to be present outside the territorial limits of the State under whose jurisdiction or control" the explosions were conducted. In accepting limitations on testing, the nuclear powers accepted as a common goal "an end to the contamination of man's environment by radioactive substances."

For more information visit the U.S. Department of State's Bureau of Nonproliferation Limited Test Ban Treaty page.