The Union of Soviet Socialist Republics (USSR), commonly known as the Soviet Union, was a transcontinental country that spanned much of Eurasia from 1922 to 1991. It was the largest country in the world by area, extending across eleven time zones and sharing land borders with twelve countries. A successor state to the Russian Empire, the country was nominally organized as a federal union of fifteen national republics, the largest and most populous of which was the Russian SFSR; in practice both its government and economy were highly centralized until its final years. It was the world's third-most populous country and Europe's most populous country. As a one-party state governed by the Communist Party of the Soviet Union, it was a flagship communist state. Its capital as well its largest city was Moscow. Other highly urbanized centers were Leningrad, Kiev, Tashkent and Baku.

The Soviet Union incorporated an area of over 22,402,200 square kilometres (8,649,500 sq mi), covering approximately one-sixth of Earth's land surface. It spanned most of Eurasia. Its largest and most populous republic was the Russian SFSR which covered roughly three-quarters of the surface area of the union, including the complete territory of contemporary Russia.