Islamic jurisprudence or usul al-fiqh provides the foundation for any meaningful study of Islamic law. The present book has been in the field for more than a decade and has received a positive response from many quarters. It is used as a textbook in a number of university courses. Over the years, however, students have shown an eagerness to know more. They have raised many questions whose answers the book did not provide. A catalogue of the questions asked, and those not asked, gave rise to the need to revise the book. The present, third, edition of the book has, therefore, been revised and three chapters at the end have been completely rewritten.