The Celle massacre (euphemistically called "Celler Hasenjagd", "hare chase of Celle") was a massacre of concentration camp inmates that took place in Celle, Prussian Hanover, in the last weeks of the Second World War. On 8 April 1945 over 3,000 internees being transported to Bergen-Belsen concentration camp were killed in an Allied air raid and subsequent attacks on survivors by SS guards, Gestapo, and Nazi party officials, as well as members of the public. Some of the perpetrators of the massacre were later tried but all of those convicted for the crime were set free in the early 1950s.

From 1933 to 1945, Nazi Germany operated more than a thousand concentration camps on its own territory and in parts of German-occupied Europe.

The first camps were established in March 1933 immediately after Adolf Hitler became Chancellor of Germany. Following the 1934 purge of the SA, the concentration camps were run exclusively by the SS via the Concentration Camps Inspectorate and later the SS Main Economic and Administrative Office. Initially, most prisoners were members of the Communist Party of Germany, but as time went on different groups were arrested, including "habitual criminals", "asocials", and Jews. After the beginning of World War II, people from German-occupied Europe were imprisoned in the concentration camps. Following Allied military victories, the camps were gradually liberated in 1944 and 1945, although hundreds of thousands of prisoners died in the death marches.

More than 1,000 concentration camps (including subcamps) were established during the history of Nazi Germany and around 1.65 million people were registered prisoners in the camps at one point. Around a million died during their imprisonment. Many of the former camps have been turned into museums commemorating the victims of the Nazi regime.