This book explores the relationship between custom and Islamic law and seeks to uncover the role of custom in the construction of legal rulings. On a deeper level, however, it deals with the perennial problem of change and continuity in the Islamic legal tradition (or any tradition for that matter). It is argued that custom (urf and adah) was one of the important tools that the jurists used to accommodate change and to adjust the rulings of shari'ah to the ever changing conditions in particular social and historical contexts. The book presents a diachronic study of the development of the concept of custom (and the different terms that have been associated with it) in the Islamic legal tradition.