This book charts the shifting boundaries of Judaism from antiquity to the modern period in order to bring clarity to what scholars mean when they claim that ancient texts or groups are “within Judaism,” as well as exploring how rabbinic Jews, Christians, and Muslims have negotiated and renegotiated what Judaism is and is not in order to form their own identities. Belief in Jesus as the Messiah was seen as part of first-century Judaism, but by the fourth or fifth century, the boundaries had...