Andrew Hayes takes the measure of Marcion's impact on second-century Christianity through a close examination of the topics and structure of Justin Martyr's writings, especially the Dialogue with Trypho, demonstrating that Justin repeatedly described Christianity in a contra-Marcionite fashion. The chief task Justin took for himself was to seize back from Marcion the terms of Christian self-definition. Marcion is thus far more important for Justin's work than the few places where he is explicitly named might suggest: they reveal Justin's deeper agenda of presenting Marcion as a demonic instrument.