Defense of St. Augustine, translated by P. De Letter, presents the enduring theological arguments of St. Prosper of Aquitaine, one of the most ardent defenders of Augustine's doctrines in the early Church. Written in the 5th century amid heated controversies over grace, free will, and predestination, Prosper's work was a direct response to critics of Augustine's teachings, particularly those who challenged his stance against Pelagianism. In this authoritative English translation, De Letter brings clarity and precision to Prosper's complex Latin prose, making it accessible to modern readers while preserving its intellectual rigor and rhetorical force. The text unfolds as a reasoned yet impassioned vindication of Augustine's theology, weaving together scriptural exegesis, theological reasoning, and appeals to Church tradition. Prosper addresses objections point by point, defending the primacy of divine grace in salvation and emphasizing the inseparability of human will and God's providence. His arguments illuminate the theological tensions of the early medieval period, offering insight into the shaping of Western Christian doctrine. This translation not only serves scholars of patristics and church history but also appeals to those interested in the development of theological thought and the enduring relevance of debates over human freedom and divine sovereignty. With De Letter's scholarly introduction and careful rendering, Defense of St. Augustine stands as both a historical document and a living voice in the ongoing conversation about faith, grace, and the nature of salvation.