The papers of this special issue have been presented during a conference that was held on January 30/31, 2014, at the University of Hamburg, organized by the ‘institute for security and prevention research’ (Institut für Sicherheits-und Präventionsforschung, ISIP). The conference was the third and last part of a series of international seminars on police and policing. While the first two seminars of this series were devoted to more general topics of European policing, the Hamburg seminar dealt with a specific question and problem of the police in Western societies, who have experienced a massive and continuing reconstitution of their social body by the entrance of a large number of people coming from foreign countries since WW II.