Oświęcim (Auschwitz) was first suggested as a site for a concentration camp for Polish prisoners by SS-Oberführer Arpad Wigand, an aide to Higher SS and Police Leader for Silesia, Erich von dem Bach-Zelewski. Bach-Zelewski had been searching for a site to house prisoners in the Silesia region, as the local prisons were filled to capacity. Richard Glücks, head of the Concentration Camps Inspectorate, sent former Sachsenhausen concentration camp commandant Walter Eisfeld to inspect the site, which already held sixteen dilapidated one-story buildings that had once served as an army barracks and a camp for transient workers. Reichsführer-SS Heinrich Himmler, head of the Schutzstaffel (SS), approved the site in April 1940, intending to use the facility to house political prisoners. SS-Obersturmbannführer (lieutenant colonel) Rudolf Höss oversaw the development of the camp and served as the first commandant. SS-Obersturmführer (senior lieutenant) Josef Kramer was appointed Höss's deputy. Auschwitz I, the original camp, became the administrative center for the whole complex.
Local residents were evicted, including 1,200 people who lived in shacks around the barracks. Around 300 Jewish residents of Oświęcim were brought in to lay foundations. From 1940 to 1941, 17,000 Polish and Jewish residents of the western districts of Oświęcim were expelled from places adjacent to the camp. The Germans also ordered expulsions from the villages of Broszkowice, Babice, Brzezinka, Rajsko, Pławy, Harmęże, Bór, and Budy. German citizens were offered tax concessions and other benefits if they would relocate to the area.  By October 1943, more than 6,000 Reich Germans had arrived. The Nazis planned to build a model modern residential area for incoming Germans, including schools, playing fields, and other amenities. Some of the plans went forward, including the construction of several hundred apartments, but many were never fully implemented. Basic amenities such as water and sewage disposal were inadequate, and water-borne illnesses were commonplace.
The first prisoners (30 German criminal prisoners from the Sachsenhausen camp) arrived in May 1940, intended to act as functionaries within the prison system. The first transport of 728 Polish prisoners, which included 20 Jews, arrived on June 14, 1940, from the prison in Tarnów, Poland. They were interned in the former building of the Polish Tobacco Monopoly, adjacent to the site, until the camp was ready. The inmate population grew quickly as the camp absorbed Poland's intelligentsia and dissidents, including the Polish underground resistance. By March 1941, 10,900 were imprisoned there, most of them Poles. ] By the end of 1940, the SS had confiscated land in the surrounding area to create a "zone of interest" about 40 square kilometres (15 sq mi) in area surrounded by a double ring of electrified barbed wire fences and watchtowers.
Construction on Auschwitz II-Birkenau began in October 1941 to ease congestion at the main camp. Reichsführer-SS Heinrich Himmler, head of the Schutzstaffel (SS), intended the camp to house 50,000 prisoners of war, who would be interned as forced laborers. Plans called for the expansion of the camp first to house 150,000 and eventually as many as 200,000 inmates.An initial contingent of 10,000 Soviet prisoners of war arrived at Auschwitz I in October 1941, but by March 1942 only 945 were still alive, and these were transferred to Birkenau, where most of them died from disease or starvation by May.By this time Hitler had decided that the Jews of Europe were to be exterminated, so Birkenau was repurposed as a combination labor camp / extermination camp.
The chief of construction of Auschwitz II-Birkenau was Karl Bischoff. Unlike his predecessor, he was a competent and dynamic bureaucrat who, in spite of the ongoing war, carried out the construction deemed necessary. The Birkenau camp, the four crematoria, the technically complicated central sauna, a new reception building, and hundreds of other buildings were planned and realized. Bischoff's plans initially called for each barrack to have an occupancy of 550 prisoners (one-third of the space allotted in other Nazi concentration camps). He later changed this to 744 prisoners per barrack. The SS designed the barracks not so much to house people as to destroy them.
The first gas chamber at Birkenau was the "red house" (called Bunker 1 by SS staff), a brick cottage converted into a gassing facility by tearing out the inside and bricking up the walls. It was operational by March 1942. A second brick cottage, the "white house" or Bunker 2, was converted some weeks later. [ These structures were in use for mass killings until early 1943 Himmler visited the camp in person on July 17 and 18, 1942. He was given a demonstration of a mass killing using the gas chamber in Bunker 2 and toured the building site of the new IG Farben plant being constructed at the nearby town of Monowitz.
In early 1943, the Nazis decided to increase greatly the gassing capacity of Birkenau. Crematorium II, originally designed as a mortuary, with morgues in the basement and ground-level incinerators, was converted into a killing factory by installing gas-tight doors, vents for the Zyklon B (a highly lethal cyanide-based pesticide) to be dropped into the chamber, and ventilation equipment to remove the gas thereafter.  It went into operation in March. Crematorium III was built using the same design. Crematoria IV and V, designed from the start as gassing centers, were also constructed that spring. By June 1943, all four crematoria were operational. Most of the victims were killed using these four structures.
Trains arrived at Auschwitz-Birkenau frequently. These transports containing Jews and other undesirables arrived from 1942 to the end of summer 1944. Between late April and early July 1944, approximately 440,000 Hungarian Jews were deported, around 426,000 of them to Auschwitz. The SS sent approximately 320,000 of them directly to the gas chambers in Auschwitz-Birkenau and deployed approximately 110,000 at forced labor in the Auschwitz concentration camp complex.
In total, approximately 1.1 million Jews were deported to Auschwitz. SS and police authorities deported approximately 200,000 other victims to Auschwitz, including 140,000-150,000 non-Jewish Poles, 23,000 Roma and Sinti (Gypsies), 15,000 Soviet prisoners of war, and 25,000 others (Soviet civilians, Lithuanians, Czechs, French, Yugoslavs, Germans, Austrians, and Italians).