From November 1933, the German criminal police had the ability to intern individuals in concentration camps based on their criminal records as part of preventive crime control. This affected several tens of thousands of people, of whom approximately 9,000 were classified as professional criminals in the Sachsenhausen concentration camp. The present volume deals with the persecution of a largely unknown group of detainees. Through individual fates, it addresses both the practices of the criminal police and the situation of professional criminals within the inmate society, as well as their exclusion from the culture of remembrance and material compensation.