Questions about the authenticity and authority of Sunna have long been of central importance to the study of Islam, especially to those concerned with Islamic law. In this study, the emergence of modern debates over Sunna is traced, focusing in particular on Egypt and Pakistan where these controversies have raged most fiercely. The implications of new approaches to the law on contemporary movements of Islamic revival are assessed. By using the case of modern Islam as a starting-point, the author considers how adherents of any great tradition deal with change and explores the impact of modernity on attitudes towards religious authority generally.