Abstract From 1933 to 1939, the Nazi concentration camps were sites of terror, torture, and deliberate killing. But they were not sites of mass murder. The early camps were designed for political repression. Within the first year of Nazi rule, about seventy concentration camps were set up, plus thirty ‘protective custody sections’ in prisons. But by mid-1934, most prisoners had been released, and the existence of the camps was in jeopardy. Why the camps survived is explained by the institutional infighting within the regime, from which the SS under Himmler emerged as victor, gaining control over the police and the camps. Soon, the camps expanded, gaining new functions: the prevention of potential resistance, the campaign against the ‘asocials’, and ‘racial general prevention’. New camps were built, and prisoner numbers rose rapidly, especially with the mass arrest of Jewish men during the November 1938 pogrom. The chapter discusses the vicious social/racial hierarchy of inmates, the role of Kapos, and the nature of performative violence. In preparation for war, from 1937 plans were made for the mass arrest of ‘unreliable types’; by now, the major purpose was to prevent another ‘November 1918’. The fate of several victims and several perpetrator biographies are outlined as exemplars. Nazi concentration camps differed radically from the colonial camps and the First World War camps: less lethal by far, so far, but nevertheless an instrument of unlimited terror to crush democracy, for social/racial engineering, and regime stabilization for imperial war.