Marc David Baer offers a new theoretical understanding of religious conversion grounded in a significant historical example - the reign of the sultan Mehmed IV (1648-87). As an expression of his turn to piety, Mehmed IV actively sought to establish his reputation as a convert-maker, convincing or coercing Christian and Jewish subjects of the Empire to be "honored by the glory of Islam". In addition, Mehmed IV and his inner circle expressed their own 'conversion' topiety and their dedication to converting others, Islamizing not only individual souls but also geographical space. Mehmed IV is remembered as an ineffectual ruler whose incompetence ultimately led to the catastrophic siege of Vienna, and Baer sheds new light on this disastrous reign by bringing to thefore the sultan's zeal for conversion.