John Wansbrough is famous for his pioneering studies on the “sectarian milieu” out of which Islam emerged. In his view, Islam grew out of different - albeit rather marginal - Jewish and Christian traditions. In the present volume, which is dedicated to Wansbrough’s memory, specialists in Islamic studies and students of the Jewish and early Christian traditions summarise Wansbrough’s achievements in the past thirty years and chart the future of the tradition study of the “sectarian milieu.”