Majdanek was a German Nazi concentration camp on the outskirts of LublinPoland, established during German Nazi occupation of Poland. The camp operated from October 1, 1941 until July 22, 1944, when it was captured nearly intact by the advancing Soviet Red Army. It was the first major concentration camp liberated by Allied forces, and the horrors found there were widely publicized. Although conceived as a forced labor camp and not as an extermination camp, over 79,000 people died there (59,000 of them Polish Jews) during the 34 months of its operation.

Among German Nazi concentration camps, Majdanek was unusual in that it was located near a major city, not hidden away at a remote rural location. It is also noted as the best-preserved concentration camp of the Holocaust: Because it was close to the former Soviet border, there was little time for the Nazis to destroy the evidence before the Red Army arrived.

"Konzentrations lager Lublin" (Concentration Camp Lublin), the official name of the Majdanek concentration camp, was established in October 1941, on Heinrich Himmler's orders to Odilo Globocnik, following the SS commander's visit to Lublin on 17 and 20 July 1941. Himmler's initial order was for a camp to hold "25,000 to 50,000" prisoners.

By mid-October 1942 the camp held 9,519 registered prisoners, of which 7,468 (or 78.45%) were Jews, and another 1,884 (19.79%) were non-Jewish Poles. By August 1943, there were 16,206 prisoners in the main camp, of which 9,105 (56.18%) were Jews and 3,893 (24.02%) were non-Jewish Poles. There were several other minority contingents including UkrainiansRussiansGermansAustriansSlovenesItalians, Belarusians, French and Dutch nationals. According to the data from the official Majdanek State Museum, 300,000 persons were inmates of the camp at one time or another. The prisoner population at any given time was much lower.

Within the general framework of Operation Reinhard, Majdanek functioned as sorting and storage depot for property and valuables taken from the victims at the killing centers in Bełżec, Sobibor, and Treblinka.  Although Majdanek also occasionally functioned as a killing center for Jews, this was initially not as systematic as in the three specifically Operation Reinhard camps: Of the more than 2,000,000 Jews killed in the course of Operation Reinhard,  59,000 (of 78,000 altogether) were killed in Majdanek.

Operation Reinhard continued until early November 1943, when the last General government Jews were exterminated as part ofOperation "Harvest festival". With respect to Majdanek, the most notorious of this wave of executions occurred on November 3, 1943 when 18,400 Jews were killed on a single day. On November 4, 25 Jews who had succeeded in hiding during the killings of the day before were found and executed. Another 611 prisoners, 311 women and 300 men, were commanded to sort through the clothes and remains of the dead. The men were at first commanded to bury the dead, but were later assigned to Sonderkommando 1005, where they had to exhume the same bodies for cremation. The men were then themselves executed. The 311 women were subsequently sent to Auschwitz where they were gassed. By the end of Operation "Harvest Festival," Majdanek had only 71 Jews left (out of a total of 6,562 prisoners).

Executions of the remaining prisoners continued at Majdanek in the months thereafter. Between December 1943 and March 1944, Majdanek received approximately 18,000 so-called "invalids," many of whom were subsequently gassed with Zyklon B (carbon monoxide was used in the very early period). Executions by firing squad continued as well, with 600 shot on January 21, 1944, 180 shot on January 23, 1944, 200 shot on March 24, 1944. 

In late July 1944, with Soviet forces rapidly approaching Lublin, the Germans hastily evacuated the camp. But the staff had only succeeded in partially destroying the crematoria before Soviet Red Army troops arrived on July 22, 1944, making Majdanek the best-preserved camp of the Holocaust. It was the first major concentration camp liberated by Allied forces, and the horrors found there were widely publicized. The 2005 research by the Head of Scientific Department at Majdanek Museum, historian Tomasz Kranz indicates that there were 78,000 victims, 59,000 of whom were Jews.