This book offers the first extensive treatment in a European language of tawba in Islam. Conventionally translated as "repentance," tawba includes the broader sense of returning to God. Khalil examines this wider notion in the early period of Sufism with a particular focus on the formative years of the tradition between Muḥāsibī and Abū Ṭālib al-Makkī. Beginning with an extensive survey of the semantic field of the term as outlined in Arabic lexicography, Khalil offers a detailed analysis of the concept in Muslim scripture. He then examines tawba as a complex psychological process involving interior conversion and a complete, unwavering commitment to the spiritual life. The ideas of five prominent figures from the first four centuries of Islam are used to illuminate the historical development of tawba and its role in early praxis-oriented Sufism.