This study applies sociological and philological analysis to the extraordinary thirteenth-century Coptic Martyrdom of John of Phanijoit. Zaborowski’s research explains the identity-shaping function behind this text’s portrayal of an Egyptian Christian’s conversion to Islam and subsequent struggle to publicly reconvert to Christianity. The heart of this book is its edition and facing English translation of the only extant manuscript of the martyrdom. Interpretive chapters include: 1) a sociological inquiry into the narrative’s depiction of Muslims; 2) a philological analysis of the Coptic language of the manuscript; and 3) an historical contextualization of the manuscript within the wider conflict between the Ayyu bids and Western Crusaders. This book makes John of Phanijoit accessible to all scholars interested in the sociology of conversion, offering new evidence for understanding Christian-Muslim relations in Medieval Egypt.