Studies of the historical Jesus typically reduce John the Baptist to a subordinate role in the story of Christian origins. This meticulous historical study focuses on John himself, revealing his extensive and enduring influence. In the popular imagination, John the Baptist plays the supporting role of Jesus's unkempt forerunner. But meticulous historical study reveals his wide-reaching and enduring influence on the history of religion. The first study of its kind, John of History, Baptist of Faith sheds light on the historical John the Baptist and his world. James F. McGrath applies historical-critical methodology not only to the New Testament but also to the Mandaean Book of John, a holy text of the last extant gnostic sect. McGrath uses the teachings of John's pupil, Jesus, as a window into his mentor's beliefs. Along the way, he brings new clarity to questions of contention among scholars, such as John's use of immersion as a substitute for temple sacrifice. Bold in its claims yet careful in its method, John of History, Baptist of Faith lends fresh insight into John, Jesus, and their world. McGrath's pioneering monograph will challenge and intrigue students and scholars of the New Testament and Second Temple Judaism.