Research on inclusive education should consider the key players: teachers. Based on three qualitative case studies of Subject teachers working in integration classes at secondary schools in Vienna, this book answers the question how inclusive education affects processes of professionalisation in teachers. The biographical approach places the Subject teachers and their biography at the centre of their professionalisation, resulting in interesting descriptions that give the reader insights into their world. The author introduces inclusive education and compares its implementation in Austria and the Netherlands. She addresses teacher professionalism in general and relates it to the concepts of Bildung and Bildungsgangforschung. The documentary method is explained and illustrated with the three case studies. Their reconstruction shows how professionalisation in relation to working in integration classes is an individual process, motivated by personal experiences, and closely linked to ideas about ones role as a teacher. Concluding, the author relates the results to international findings and gives suggestions for implementing inclusive education. Die Studie wurde im Jahr 2022 ausgezeichnet mit dem Dissertationspreis der Österreichischen Gesellschaft für Forschung und Entwicklung im Bildungswesen (ÖFEB).