The twentieth century was “short”, running only from 1914 to 1990/1991. Even so, it will doubtless enter history as an unprecedented era of dictatorships. The question of how these totalitarian regimes functioned in practice, how and to what extent they were able to realize their power aspirations, has until now been answered empirically at most highly selectively. Extensive comparative research efforts will be required over the coming decades. The police as the key organization in the state monopoly of power is particularly important in this context, since like no other institution it operates at the interface of state and society. Using the example of the Gestapo's activities in the Third Reich, this article analyses collaboration structures between these two spheres, which made possible (either on a voluntary or coercive basis) a penetration of social contexts and hence police action even in shielded areas. It is my thesis that such exchange processes through unsolicited denunciation and informers with double identities will also have been decisive outside Germany in the tracking of dissident behaviour and the detection of conspiratorial practices.