TURKISH ISLAMIC STUDIES series (TISs) For over two centuries, scholars in Türkiye have produced a rich and sophisticated body of work across Islamic sciences and intellectual history. Yet this scholarship has remained insufficiently visible in global academic discourse, while Western and Orientalist studies have long circulated widely in Turkish translation.The Turkish Islamic Studies series (TISs) responds to this imbalance by introducing major works of Turkish Islamic scholarship to international readers through carefully supervised English translations. The series aims to foster a more reciprocal exchange of knowledge and to open Türkiye's Islamic scholarly heritage to the world. About this Volume In The Book of al-Sunna, Musa Jarullah Bigiyev presents one of his most systematic late reflections on the authority, scope, and function of the Prophetic Sunna in Islamic thought. Written against approaches that sought to confine religious authority to the Qurʾān alone, the work argues that the Sunna occupies a foundational position among the sources of Islamic law and religious knowledge. Bigiyev examines the meaning of Sunna, the Qurʾānic portrait of the Prophet's sīra, the evidentiary authority of Prophetic practice, and the role of āḥād reports. He also discusses knowledge and its means of acquisition, the relationship between reason and transmission, legal evidences, qiyās, causation, induction, custom, social experience, necessity, historical testimony, and the guidance of reason. By uniting revelation, law, reason, communal authority, and religious renewal, this volume presents Bigiyev's mature attempt to articulate a dynamic yet textually grounded understanding of the Sunna for the modern Muslim world. Opening Türkiye's Islamic scholarship to the world.