The Roman Empire’s approach to religion has traditionally been described in ambiguous terms. On the one hand, Rome has often been regarded as almost proverbially tolerant, as well as highly flexible in its dealings with the diverse range of religious cults and practices within its territories. On the other hand, the Roman religious landscape was not without its limits, and there were certain groups who found themselves, for one reason or another, on the outside. Within scholarship, however, the legal interactions between such groups and the Roman authorities have widely been studied in isolation. This book instead takes a comparative approach, and investigates how members of various marginalized religious groups were embedded in, and interacted with, the wider Roman legal system. It compares and contrasts the legal treatment of private diviners, Jewish communities, and early Christians, and in doing so aims to provide a broader perspective on the legal treatment of marginalized religion in the Roman world. The study suggests that the known interactions between these respective groups and the Roman authorities are best understood within the wider context of Roman law and administration, and argues that they furthermore shared a number of important characteristics. While the treatment these groups received was certainly not in all respects identical, the procedural, socio-political, and ideological mechanisms that underpinned the relevant legal measures were nonetheless conspicuously similar.