Sects and sectarianism are popular themes in Jewish history, but the meaning of these terms is elusive, often raising more problems than solutions. This volume, drawing on the expertise of a wide range of scholars, examines several Jewish groups from Antiquity to the present day that have been traditionally identified as ‘sects’ or as ‘sectarian’, including most famously the Qumran community and the Qaraites. It questions whether ‘sect’ and ‘sectarianism’ are appropriate or effective as historical categories for the interpretation of social and religious movements in Jewish history.