The Soviet atomic bomb project was the classified research and development program that was authorized by Joseph Stalin in the Soviet Union to develop nuclear weapons during and after World War II. Although the Soviet scientific community discussed the possibility of an atomic bomb throughout the 1930s, going as far as making a concrete proposal to develop such a weapon in 1940, the full-scale program was not initiated and prioritized until Operation Barbarossa.

After Stalin learned of the atomic bombings of Hiroshima and Nagasaki, the program was pursued aggressively and accelerated through effective intelligence gathering about the German nuclear weapon project and the American Manhattan Project. The Soviet efforts also rounded up captured German scientists to join their program, and relied on knowledge passed by spies to Soviet intelligence agencies.

On 29 August 1949, the Soviet Union secretly conducted its first successful weapon test (First Lightning, based on the American "Fat Man" design) at the Semipalatinsk-21 in Kazakhstan. Stalin alongside Soviet political officials and scientists were elated at the successful test. A nuclear armed Soviet Union sent its rival Western neighbors, and particularly the United States into a state of unprecedented trepidation. From 1949 onwards the Soviet Union manufactured and tested nuclear weapons on a large scale. Its nuclear capabilities served as an important role on its global status. A nuclear armed Soviet Union escalated the Cold War with the United States to the possibility of nuclear war and ushered in the doctrine of mutually assured destruction.