This volume presents case studies of the phenomena that contributed to group identity in late antique Syria-Mesopotamia, in particular traditions reflecting interactions between Judaism and Christianity, among various Christian groups, and among other religious traditions of late antiquity (such as Zoroastrianism or 'paganism'). By studying Christian, Jewish and other sources that deal with the establishment, modification and deletion of boundaries, the authors seek to create a frame of reference that will in turn explain and contextualise the existing evidence concerning communication and interaction between highly diverse groups in Late Antiquity.