The present volume focuses on aspects of Islamic thought in Iran and Yemen, and other regions of the Middle East, ninth through fifteenth century CE, through a close study of manuscript materials. The book's sixteen chapters are arranged under five rubrics: Mu'tazilism, Zaydism in Iran and in Yemen, Twelver Shi'ism, Mysticism, and Bibliographical Traditions. The material included in the book has been published previously in a different version. The appearance of these studies together in a single volume makes this book a significant and welcome contribution to the field of classical Islamic Studies.