The Gulag was a system of forced labor camps in the Soviet Union. The word Gulag originally referred only to the division of the Soviet secret police that was in charge of running the forced labor camps from the 1930s to the early 1950s during Joseph Stalin's rule, but in English literature the term is popularly used for the system of forced labor throughout the Soviet era. The abbreviation GULAG (ГУЛАГ) stands for "Glávnoye upravléniye ispravítel'no-trudovýkh lageréy " (Гла́вное управле́ние исправи́тельно-трудовы́х лагере́й or "Main Directorate of Correctional Labour Camps"), but the full official name of the agency changed several times.

The Gulag is recognized as a major instrument of political repression in the Soviet Union. The camps housed both ordinary criminals and political prisoners, a large number of whom were convicted by simplified procedures, such as NKVD troikas or other instruments of extrajudicial punishment. The agency was established in 1930 and initially was administered by the OGPU (1923–1934), later known as the NKVD (1934–1946), and the Ministry of Internal Affairs (MVD) in the final years.

The internment system grew rapidly, reaching a population of 100,000 in the 1920s. By the end of 1940, the population of the Gulag camps amounted to 1.5 million. The emergent consensus among scholars is that, of the 14 million prisoners who passed through the Gulag camps and the 4 million prisoners who passed through the Gulag colonies from 1930 to 1953, roughly 1.5 to 1.7 million prisoners perished there or died soon after they were released. Some journalists and writers who question the reliability of such data heavily rely on memoir sources that come to higher estimations.