During the Second World War, Nazi-Germany used the Geheime Staatspolizei (Gestapo) in its occupied territories and at the home front to maintain order and execute the racial policy of the regime. With a head office in Brussels and branches in Antwerp, Ghent, Liège and Charleroi, the Gestapo was also present in military occupied Belgium. The German agents were not completely up to their task. They lacked the knowledge of the regional languages and circumstances. The help of the local Belgian populace was therefore a necessity. What motivated these men to collaborate so assiduously with the German occupier? This research is based on the postwar criminal case files, compiled by the military courts in the context of the prosecution of those who collaborated. Several biographies of Flemish collaborators with the Gestapo office in Antwerp have been reconstructed. In this way, four major motivational groups can be distinguished: opportunists, ideological perpetrators, ‘traditional’ collaborators and former members of the resistance. Contrary to existing research into similar groups of men, financial or material gain was not their primary motive. Various psychological factors played a greater role.