The City of God is a book of Christian philosophy presenting human history as a conflict between what Augustine calls the Earthly City and the City of God-a conflict that is destined to end in victory for the latter. The City of God is marked by people who forego earthly pleasure to dedicate themselves to the eternal truths of God, now revealed fully in the Christian faith. The Earthly City, on the other hand, consists of people who have immersed themselves in the cares and pleasures of the present, passing world.

The City of God was written in response to allegations that Christianity brought about the decline of Rome. It is considered one of Augustine's most important works, standing alongside The Confessions, The Enchiridion, On Christian Doctrine, and On the Trinity. As a work of one of the most influential Church Fathers, The City of God is a cornerstone of Western thought, presenting many profound questions of theology, such as the suffering of the righteous, the existence of evil, the conflict between free will and divine omniscience, and the doctrine of original sin.