Jewish law in connection with the circumcision debate, Islamic law in the debate over the burka ban or the slaughtering of animals, the law of the Christian churches applying to the appointment of bishops, or questions of employment law within the church - the internal law of the religions is increasingly becoming a topic of public debate and conflict. Questions of religious law affect educational institutions, hospitals, prisons, police work and numerous other aspects of everyday life.In this context, comparison of the internal law of the religions is developing as a new specialist discipline combining theology, jurisprudence and religious studies. The author introduces the subject and methodology based on previous research approaches. Along with an overview of law in various confessions and religions, he demonstrates how such law can be placed within the secular law of the European states. This practically oriented introduction presents comprehensive theoretical approaches and practical areas of application for the first time in the German-speaking countries.