Operation Reinhard or Operation Reinhardt was the codename of the secret German plan in World War II to exterminate Polish Jews in the General Government district of German-occupied Poland. This deadliest phase of the Holocaust was marked by the introduction of extermination camps. The operation proceeded from March 1942 to November 1943; about 1.47 million or more Jews were murdered in just 100 days from late July to early November 1942, a rate which is approximately 83% higher than the commonly suggested figure for the kill rate in the Rwandan genocide. In the time frame of July to October 1942, the overall death toll, including all killings of Jews and not just Operation Reinhard, amounted to two million killed in those four months alone. It was the single fastest rate of genocidal killing in history.

The occupation of Poland by Nazi Germany and the Soviet Union during World War II (1939–1945) began with the Invasion of Poland in September 1939, and it was formally concluded with the defeat of Germany by the Allies in May 1945. Throughout the entire course of the occupation, the territory of Poland was divided between Nazi Germany and the Soviet Union (USSR), both of which intended to eradicate Poland's culture and subjugate its people. In the summer-autumn of 1941, the lands which were annexed by the Soviets were overrun by Germany in the course of the initially successful German attack on the USSR. After a few years of fighting, the Red Army drove the German forces out of the USSR and crossed into Poland from the rest of Central and Eastern Europe.