'Aktion Erntefest' was a German operation for the mass killing at the Maidanek extermination camp and its sub-camps for the destruction of all remaining Polish Jews in the Lublin district and the Lublin ghetto within the Generalgouvernement, including the entire slave-labour camp work force (3 November 1943).

About 43,000 Jews were killed on the instruction of two SS officers, SS-Gruppenführer Jakob Sporrenberg and SS-Sturmbannführer Christian Wirth, as the conclusion of 'Reinhard' (i). 'Aktion Erntefest' was the single largest German massacre of Jews in the entire war, and resulted in the deaths of 10,000 persons more than at the Babi Yar massacre outside Kiev, and was exceeded only by the 1941 Odessa massacre by Romanian troops of more than 50,000 Jews in October 1941.

The timing of the operation seemed to have been the response of the SS to several resistance efforts by surviving Jews: examples are the uprisings in the Sobibor and Treblinka extermination camps, and armed resistance in the Warsaw, Białystok and Vilna ghettos. The SS feared additional Jewish-led revolts in the Generalgouvernement as Soviet counter-offensives started to drove the Eastern Front back to the west. To prevent the threat of further resistance, the SS decided to kill the remaining Jews even though these were employed in the slave-labour projects of the Ostindustrie (Osti) enterprise, which was owned by the SS, at the Trawniki, Poniatowa and Maidanek concentration camps with sub-camps at Budzyn, Kraśnik, Puławy, Lipowa and other places.

Unaware of the real purpose to which their largest effort was to be put, the inmates were ordered to dig anti-tank trenches, and 'Aktion Erntefest' began at dawn on 3 November. The main camp at Maidanek and the sub-camps at Trawniki and Poniatowa were surrounded by SS men and the 101^st Polizei Reserveabteilung (a unit of the Ordnungspolizei from Hamburg) augmented by 'Hiwis' (Trawniki men). The Jews were then taken out of the camps in groups and shot. At Maidanek the Jews had first been separated from the other prisoners, and were taken in groups to long and deep trenches and shot individually under the leadership of SS-Oberscharführer Eric Muhsfeldt.

At the main camp, 18,400 Jews were killed on 3 November, and Jews from other slave labor camps in the Lublin area were also taken to Maidanek and shot. The massacre was completed in a single day at Majdanek and Trawniki. At Poniatowa the shootings took two days, because in one of the barracks the Jews resisted. The SS set fire to this barrack building and the killings went on as planned.