The files of the Ciechanów (Zichenau) Gestapo – one of the few remaining archives of this kind from German-occupied Poland – offer interesting insights into the social policy of the Nazi state. The Germanisation of Polish territories occurred by deporting and exterminating the Jews, depriving Poles of their rights and supporting the local Germans and the ethnic Germans resettled from the East. The German minority living in this ethnically mixed region was required to adhere to strict codes of behaviour and was held accountable for all unauthorised contacts with their Polish and, even more so, their Jewish neighbours. The system of control and repression strove to isolate the various ethnic (‘racial’) groups, encouraging denunciations and thus instilling fear in the populace. This article pays particular attention to the actions of German citizens who fell under the scrutiny of the Secret Police.