Citizens of the Earth presents the first comprehensive account of Augustine's engagement with traditional Roman religion. A multifaceted case-study in the Christianization of the Roman Empire, it anchors Augustine's works in their intellectual and social context, narrating political and intellectual renegotiation of the public cults of North Africa from the 390s until after Augustine's death in 430. At the same time, it tests modern conceptions of the role of religious conviction and religious difference in late antique society against the ideas of one of the most influential late Roman thinkers. Approaching Augustine simultaneously as thinker, practical preacher, and observer of his North African world, Citizens of the Earth synthesizes Augustine's ideas about religion from sermons and treatises, describes how his polemical approach to the Roman gods developed across his career, and reconstructs competing ideas developed by his interlocutors. It emphasizes pagan conviction and lay religiosity, argues that we should see Augustine's polemics as attempts at practical outreach and persuasion, and stresses the importance of conversion for understanding the pagan-Christian boundary. The book closes with both historical and theoretical conclusions. After proposing that the Vandalic conquest of Carthage (439) marked a final ending point for traditional, public religiosity in North Africa, it considers how Augustine's contributions can still inform modern approaches to late antique religion.