This book is a comprehensive historical overview of the formative period of Sufism, the major mystical tradition in Islam, from the ninth to the twelfth century C.E. Ahmet T. Karamustafa bases his study on a fresh reading of the primary sources as well as recent scholarship on the subject and presents a unified narrative of Sufism's historical development. His innovative analytical framework reveals the emergence of mystical currents in Islam during the ninth century and traces the rapid spread of Iraq-based Sufism to other regions of the Islamic world. The book also describes Sufism's fusion with indigenous mystical movements elsewhere and extensively analyzes the formation of Sufi communities, Sufi sainthood, and the nonconformist dimensions of Sufism.