The following closely related categories of forced labor in the Soviet Union may be distinguished.
Pre-Gulag forced labor of the early Soviet Russia and Soviet Union
The Gulag system,
The kolkhoz system
The Stroybat (construction battalions) system,
Foreign forced labor in the Soviet Union of 1939-1954 which included forced labor of World War II prisoners of war and internees.
Post-Joseph Stalin penal labor in the Soviet Union: Corrective labor colony (Исправительно-трудовая колония, ИТК), Colony-settlement (Колония-поселение), corrective labor without incarceration (Исправительные работы без лишения свободы).