A comprehensive and authoritative account of the 'heretic' Marcion, this volume traces the development of the concept and language of heresy in the setting of an exploration of second-century Christian intellectual debate. Judith M. Lieu analyses accounts of Marcion by the major early Christian polemicists who shaped the idea of heresy, including Justin Martyr, Irenaeus, Tertullian, Epiphanius of Salamis, Clement of Alexandria, Origen, and Ephraem Syrus. She examines Marcion's Gospel, Apostolikon, and Antitheses in detail and compares his principles with those of contemporary Christian and non-Christian thinkers, covering a wide range of controversial issues: the nature of God, the relation of the divine to creation, the person of Jesus, the interpretation of Scripture, the nature of salvation, and the appropriate lifestyle of adherents. In this innovative study, Marcion emerges as a distinctive, creative figure who addressed widespread concerns within second-century Christian diversity.