The occupation of the Baltic states refers to the occupation of the Baltic states (Estonia, Latvia, and Lithuania) first by the Soviet Union under the provisions of the 1939 Molotov-Ribbentrop Pact with Nazi Germany, by Nazi Germany from 1941-1944, and again by the Soviet Union from 1944-91.

When World War II started in September 1939, the fate of the Baltic countries had been already decided in the German-Soviet Nonaggression Pact and its Secret Additional Protocol of August 1939.

World War II losses in the Baltic states were among the highest in Europe. Estimates of population loss stand at 25% for Estonia, 30% for Latvia, and 15% for Lithuania. War and occupation deaths have been estimated at 90,000 in Estonia, 180,000 in Latvia, and 250,000 in Lithuania. These include the Soviet deportations in 1941, the German deportations, and Holocaust victims.

In the reassessment of Soviet history that began during perestroika, in 1989 the USSR condemned the 1939 secret protocol between Nazi Germany and itself that had led to the invasion and occupation of the three Baltic countries.

The Baltic States' struggle for independence came to a conclusion in 1991, when the sovereignties of the countries were restored, contributing to the eventual break-up of the Soviet Union later that year after the three states had seceded. The last Russian troops withdrew from the Baltic States in August 1994.