Many of the horrors associated with Auschwitz—gas chambers, medical experiments, working prisoners to death—had been pioneered in earlier concentration camps. In the late thirties, driven largely by Himmler’s ambition to make the S.S. an independent economic and military power within the state, the K.L. began a transformation from a site of punishment to a site of production. The two missions were connected: the “work-shy” and other unproductive elements were seen as “useless mouths,” and forced labor was a way of making them contribute to the community. Oswald Pohl, the S.S. bureaucrat in charge of economic affairs, had gained control of the camps by 1938, and began a series of grandiose building projects. The most ambitious was the construction of a brick factory near Sachsenhausen, which was intended to produce a hundred and fifty million bricks a year, using cutting-edge equipment and camp labor.
Action T4 was a programme of systematic murder of the physically and mentally handicapped and patients in psychiatric hospitals that took place mainly from 1939 to 1941, and continued until the end of the war. Initially the victims were shot by the Einsatzgruppen and others; gas chambers and gas vans using carbon monoxide were used by early 1940.[312][313] Under the Law for the Prevention of Hereditarily Diseased Offspring, enacted on 14 July 1933, over 400,000 individuals underwent compulsory sterilisation.[314] Over half were those considered mentally deficient, which included not only people who scored poorly on intelligence tests, but those who deviated from expected standards of behaviour regarding thrift, sexual behaviour, and cleanliness. Most of the victims came from disadvantaged groups such as prostitutes, the poor, the homeless, and criminals.[315] Other groups persecuted and killed included Jehovah's Witnesses, homosexuals, social misfits, and members of the political and religious opposition.[186][316]
German business leaders disliked Nazi ideology but came to support Hitler, because they saw the Nazis as a useful ally to promote their interests.[54] Business groups made significant financial contributions to the Nazi Party both before and after the Nazi seizure of power, in the hope that a Nazi dictatorship would eliminate the organized labour movement and the left-wing parties.[55] Hitler actively sought to gain the support of business leaders by arguing that private enterprise is incompatible with democracy.[56]

After examining several sites for a new plant to manufacture Buna-N, a type of synthetic rubber essential to the war effort, the German chemical cartel IG Farben chose a site near the towns of Dwory and Monowice (Monowitz in German), about 7 kilometres (4.3 mi) east of Auschwitz I.[50] Tax exemptions were available to corporations prepared to develop industries in the frontier regions under the Eastern Fiscal Assistance Law, passed in December 1940. The site had good railway connections and access to raw materials.[51] In February 1941, Himmler ordered that the Jewish population of Oświęcim be expelled to make way for skilled laborers; that all Poles able to work remain in the town and work on building the factory; and that Auschwitz prisoners be used in the construction work.[52]
Around 7,000 SS personnel were posted to Auschwitz during the war.[84] Of these, 4 percent of SS personnel were officers and 26 percent were non-commissioned officers, while the remainder were rank-and-file members.[85] Camp guards were members of the SS-Totenkopfverbände (Death's Head Units).[86] Approximately three in four SS personnel worked in security. Others worked in the medical or political departments, in the camp headquarters, or in the economic administration, which was responsible for the property of dead prisoners.[85] SS personnel at the camp included 200 women, who worked as guards, nurses, or messengers.[80] About 120 SS personnel were assigned to the gas chambers and lived on site at the crematoria.[87]

Of those who received numbers at Auschwitz-Birkenau, only 65,000 survived. It is estimated that only about 200,000 people who passed through the Auschwitz camps survived. Michael Bornstein was one of the lucky ones. Decades after the war, he learned from Auschwitz documents kept in Israel that he had survived because he was sick and the Nazis left him behind when they evacuated the camp. He said that he was one of only 52 children under the age of eight who lived.
Despite such tactical breaks necessitated by pragmatic concerns, which were typical for Hitler during his rise to power and in the early years of his regime, Hitler never ceased being a revolutionary dedicated to the radical transformation of Germany, especially when it concerned racial matters. In his monograph, Hitler: Study of a Revolutionary?, Martyn Housden concludes:
Ms. Jastrzebiowska’s husband, Andrzej Jastrzebiowski, 38, is a metal conservator. He spent three months cleaning all the eyeglasses in a vitrine, preserving their distressed state but trying to prevent them from corroding further. “When I saw the eyeglasses in the exhibition, I saw it as one big pile,” he said. But in the lab, he began to examine them one by one. One had a screw replaced by a bent needle; another had a repaired temple. “And then this enormous mass of glasses started becoming people,” Mr. Jastrzebiowski said. This “search for the individual,” he said, helps ensure that the work does not become too routine.
SS officers, including the infamous Dr. Josef Mengele, would conduct selections among these lines, sending most victims to one side and thus condemning them to death in the gas chambers. A minority was sent to the other side, destined for forced labor. Those who were sent to their deaths were killed that same day and their corpses were burnt in the crematoria. Those not sent to the gas chambers were taken to “quarantine,” where their hair was shaved, striped prison uniforms distributed, and registration took place. Prisoners’ individual registration numbers were tattooed onto their left arm.

The complex, which divided into three main areas, was established by the Nazi’s in 1940 and was in use until its Allied liberation in 1945. Historians and analysts estimate the number of people murdered at Auschwitz somewhere between 2.1 million to 4 million, of whom the vast majority were Jews. The majority of prisoners held at Auschwitz were killed in the various gas chambers though many died from starvation, forced labor, disease, shooting squads, and heinous medical experiments.
The chief of construction of Auschwitz II-Birkenau was Karl Bischoff, a competent and dynamic bureaucrat who, in spite of the ongoing war, carried out the construction deemed necessary. The Birkenau camp, the four crematoria, a new reception building, and hundreds of other buildings were planned and constructed.[42] Bischoff's plans, based on an initial budget of RM 8.9 million, called for each barracks to hold 550 prisoners. He later changed this to 744 per barracks, which meant the camp could hold 125,000, rather than 97,000.[43] The SS designed the barracks not so much to house people as to destroy them.[42] There were 174 barracks, each measuring 116 by 36 ft, divided into 62 bays of 43 sq. ft. The bays were divided into "roosts", initially for three inmates and later for four. With personal space of 11 sq. ft to sleep and place whatever belongings they had, inmates were deprived, Robert-Jan van Pelt wrote, "of the minimum space needed to exist".[44]

“It's utterly impossible for me to build my life on a foundation of chaos, suffering and death. I see the world being slowly transformed into a wilderness; I hear the approaching thunder that, one day, will destroy us too. I feel the suffering of millions. And yet, when I look up at the sky, I somehow feel that everything will change for the better, that this cruelty too shall end, that peace and tranquility will return once more.”

One of the first people I encountered was Mengele. He told us to undress and stand in line and he went through the ranks deciding who was strong and healthy and fit for work, and who was only fit for the gas chamber. After inspecting me, he put his thumb up high, so they gave me the striped uniform and sent me to get a number tattooed on to my arm. I don’t remember the number. It’s there still, but I never look at it because it brings back too many painful memories.
Auschwitz was considered a comfortable posting by many SS members, because of its many amenities.[84] SS personnel were initially allowed to bring partners, spouses, and children to live at the camp, but when the SS camp grew more crowded, Höss restricted further arrivals. Facilities for the SS personnel and their families included a library, swimming pool, coffee house, and a theater that hosted regular performances.[80]
In Auschwitz and Majdanek, which had the role of both being a working and an extermination camp, Jews were divided upon arrival into those capable of working ands those not. The last group was sent directly to the gas chambers, whereas those able to work had to work themselves to death in SS’s industries – or they were executed when they worn down. In Auschwitz, the Jews worked in the so-called Monowitz working camp (Auschwitz III) in factories, or they were hired out to private businesses such as the chemical corporation I.G. Farben or the SS’s own factories.
Besides tormenting us physically, the S. S. guard continually tried to torment us morally. Coming partly from the lowest proletariat, they tried to annoy us with quotations from the Stürmer. They asked us about the accuracy of supposed quotations from the Talmud which are purported to order the Jew to hate other nations, and especially all Christians. They had little success with these questions, since the prisoners had to answer almost without exception that they did not know more than the name of the Talmud.
Nine out of 10 victims in Auschwitz-Birkenau were Jews. The remaining victims were mainly Poles, gypsies, and Soviet POW’s. Majdanek began its gassings in October 1942. The camp functioned in the same way as Auschwitz-Birkenau, and also included a concentration- and work camp. In the autumn of 1943 the camp was closed after claiming between 60,000 and 80,000 Jewish victims.
Some of the most notorious slave labour camps included a network of subcamps. Gross-Rosen had 100 subcamps,[37] Auschwitz had 44 subcamps,[38][38][39] Stutthof had 40 sub-camps set up contingently.[40] Prisoners in these subcamps were dying from starvation, untreated disease and summary executions by the tens of thousands already since the beginning of war.[41]