Sobibor (/ˈsoʊbɪbɔːr/ SOH-bi-bor; Polish: Sobibór [sɔˈbibur]; German: [ˈzoːbibɔʁ]) was an extermination camp built and operated by Nazi Germany as part of Operation Reinhard. It was located in the forest near the village of Żłobek Duży in the General Government region of German-occupied Poland.

As an extermination camp rather than a concentration camp, Sobibor existed for the sole purpose of murdering Jews. The vast majority of prisoners were gassed within hours of arrival. Those not killed immediately were forced to assist in the operation of the camp, and few survived more than a few months. In total, some 170,000 to 250,000 people were murdered at Sobibor, making it the fourth-deadliest Nazi camp after Auschwitz, Treblinka, and Belzec.

The camp ceased operation after a prisoner revolt which took place on 14 October 1943. The plan for the revolt involved two phases. In the first phase, teams of prisoners were to discreetly assassinate each of the SS officers. In the second phase, all 600 prisoners would assemble for evening roll call and walk to freedom out the front gate. However, the plan was disrupted after only eleven SS men had been killed. The prisoners had to escape by climbing over barbed wire fences and running through a mine field under heavy machine gun fire. About 300 prisoners made it out of the camp, of whom roughly 60 survived the war.

After the revolt, the Nazis demolished most of the camp in order to hide their crimes from the advancing Red Army. In the first decades after World War II, the site was neglected and the camp had little presence in either popular or scholarly accounts of the Holocaust. It became better known after it was portrayed in the TV miniseries Holocaust (1978) and the film Escape from Sobibor (1987). The Sobibor Museum now stands at the site, which continues to be investigated by archaeologists. Photographs of the camp in operation were published in 2020 as part of the Sobibor perpetrator album.

Sobibor was one of four extermination camps established as part of Operation Reinhard, the deadliest phase of the Holocaust. The extermination of Europe's Jews did not originate as a single top-down decision, but was rather a patchwork of decisions made regarding particular occupied areas. Following the invasion of Poland in September 1939, the Germans began implementing the Nisko Plan in which Jews were deported from ghettos across Europe to the forced labour camps which comprised the Lublin Reservation. Lublin District region was chosen in particular for its inhospitable conditions. The Nisko Plan was abandoned in 1940 but many forced labour camps continued operations in the area, including Trawniki, Lipowa 7, and Dorohucza.

In 1941, the Nazis began experimenting with gassing Jews. In December 1941, SS officials at Chełmno conducted experiments using gas vans and the first mass gassings were conducted at Auschwitz concentration camp in January. At the Wannsee Conference on 20 January 1942, Reinhard Heydrich announced a plan for systematically murdering the Jews through a network of extermination camps. This plan was realized as Operation Reinhard.

Nothing is known for certain about the early planning for Sobibor in particular. Some historians have speculated that planning began as early as 1940, on the basis of a railway map from that year which omits several major cities but includes Sobibór and Bełżec. The earliest hard evidence for Nazi interest in the site comes from the testimony of local Poles, who noticed in Autumn 1941 that SS officers were surveying the land opposite the train station. When a worker at the station cafeteria asked one of the SS men what was being built, he replied that she would soon see and that it would be "a good laugh."

In March 1942, SS-Hauptsturmführer Richard Thomalla took over construction work at Sobibor, which had begun at an unknown earlier date. Thomalla was a former building contractor and committed Nazi whose service as an auxiliary police commander and adviser on Jewish forced labour had earned him a high-ranking position in Odilo Globočnik's construction department. Having previously overseen the construction of Bełżec extermination camp, he applied lessons learned there to Sobibor. Thomalla allotted a much larger area for Sobibor than he had for Bełżec, allowing more room to maneuver as well as providing space for all of the camp's facilities to be constructed within its perimeter.