Auschwitz concentration camp (German: Konzentrationslager Auschwitz (pronounced [kntsntatsionsla avts] (listen)); also KL Auschwitz or KZ Auschwitz) was a complex of over 40 concentration and extermination camps operated by Nazi Germany in occupied Poland (in a portion annexed into Germany in 1939) during World War II and the Holocaust. It consisted of Auschwitz I, the main camp (Stammlager) in Owicim; Auschwitz II-Birkenau, a concentration and extermination camp with gas chambers; Auschwitz III-Monowitz, a labor camp for the chemical conglomerate IG Farben; and dozens of subcamps. The camps became a major site of the Nazis' final solution to the Jewish question.

After Germany sparked World War II by invading Poland in September 1939, the Schutzstaffel (SS) converted Auschwitz I, an army barracks, into a prisoner-of-war camp.The initial transport of political detainees to Auschwitz consisted almost solely of Poles for whom the camp was initially established. The bulk of inmates were Polish for the first two years.In May 1940, German criminals brought to the camp as functionaries, established the camp's reputation for sadism. Prisoners were beaten, tortured, and executed for the most trivial reasons. The first gassingsof Soviet and Polish prisonerstook place in block 11 of Auschwitz I around August 1941. Construction of Auschwitz II began the following month, and from 1942 until late 1944 freight trains delivered Jews from all over German-occupied Europe to its gas chambers. Of the 1.3 million people sent to Auschwitz, 1.1 million were murdered. The number of victims includes 960,000 Jews (865,000 of whom were gassed on arrival), 74,000 ethnic Poles, 21,000 Roma, 15,000 Soviet prisoners of war, and up to 15,000 other Europeans. Those not gassed were murdered via starvation, exhaustion, disease, individual executions, or beatings. Others were killed during medical experiments.

At least 802 prisoners tried to escape, 144 successfully, and on 7 October 1944 two Sonderkommando units, consisting of prisoners who operated the gas chambers, launched an unsuccessful uprising. Only 789 Schutzstaffel personnel (no more than 15 percent) ever stood trial after the Holocaust ended; several were executed, including camp commandant Rudolf Hss. The Allies' failure to act on early reports of atrocities by bombing the camp or its railways remains controversial.

As the Soviet Red Army approached Auschwitz in January 1945, toward the end of the war, the SS sent most of the camp's population west on a death march to camps inside Germany and Austria. Soviet troops entered the camp on 27 January 1945, a day commemorated since 2005 as International Holocaust Remembrance Day. In the decades after the war, survivors such as Primo Levi, Viktor Frankl, and Elie Wiesel wrote memoirs of their experiences, and the camp became a dominant symbol of the Holocaust. In 1947, Poland founded the Auschwitz-Birkenau State Museum on the site of Auschwitz I and II, and in 1979 it was named a World Heritage Site by UNESCO.

Rudolf "Rudi" Vrba (born Walter Rosenberg; 11 September 1924 – 27 March 2006) was a Slovak-Jewish biochemist who, as a teenager in 1942, was deported to the Auschwitz concentration camp in German-occupied Poland. He became known for having escaped from the camp in April 1944, at the height of the Holocaust, and for having co-written a detailed report about the mass murder that was taking place there. Distribution of the report by George Mantello in Switzerland is credited with having halted the mass deportation of Hungary's Jews to Auschwitz in July 1944, saving more than 200,000 lives. After the war Vrba trained as a biochemist, working mostly in England and Canada.Vrba and fellow escapee Alfréd Wetzler fled Auschwitz three weeks after German forces invaded Hungary and shortly before the SS began mass deportations of Hungary's Jewish population to the camp. The information the men dictated to Jewish officials when they arrived in Slovakia on 24 April 1944, which included that new arrivals in Auschwitz were being gassed and not "resettled" as the Germans maintained, became known as the Vrba–Wetzler report. When the War Refugee Board published it with considerable delay in November 1944, the New York Herald Tribune described it as "the most shocking document ever issued by a United States government agency". While it confirmed material in earlier reports from Polish and other escapees, the historian Miroslav Kárný wrote that it was unique in its "unflinching detail".There was a delay of several weeks before the report was distributed widely enough to gain the attention of governments. Mass transports of Hungary's Jews to Auschwitz began on 15 May 1944 at a rate of 12,000 people a day. Most went straight to the gas chambers. Vrba argued until the end of his life that the deportees might have refused to board the trains, or at least that their panic would have disrupted the transports, had the report been distributed widely and sooner.From late June and into July 1944, material from the Vrba–Wetzler report appeared in newspapers and radio broadcasts in the United States and Europe, particularly in Switzerland, prompting world leaders to appeal to Hungarian regent Miklós Horthy to halt the deportations. On 2 July American and British forces bombed Budapest, and on 6 July, in an effort to exert his sovereignty, Horthy ordered that the deportations should end. By then, over 434,000 Jews had been deported in 147 trains—almost the entire Jewish population of the Hungarian countryside—but another 200,000 in Budapest were saved.