Avi Sagi and Zvi Zohar have, in recent years, made great contributions to Jewish studies, in particular the study of halakhah. In their many individual publications they have mined the often ignored halakhic literature in order to offer perspectives in a variety of areas. They have also jointly published a number of works, including a very learned study on conversion (Giyur ve–Zehut Yehudit). In their latest work, Circles of Jewish Identity: A Study in Halakhic Literature, they follow the path set out in their previous work by asking what the assumptions and conclusions of halakhic literature tell us about issues of Jewish identity, such as how to define it; whether it is immutable; and, if not immutable, whether one's Jewish identity can be removed against one's will. Their discussion proceeds from the relevant talmudic texts, through the medieval period, up until the most recent responsa. This chronological approach is helpful in charting the development of concepts.