Augustine of Hippo (354–430 AD), also known as Saint Augustine, was a theologian, bishop, and philosopher whose writings shaped the course of Western Christianity and medieval philosophy. Born in Thagaste, Roman North Africa (present-day Algeria), he was ordained Bishop of Hippo Regius in 395 AD and held that office until his death. He is recognized as a Doctor of the Church in Roman Catholicism and is venerated as a saint in Catholic, Eastern Orthodox, and Anglican traditions. His influence extends into secular philosophy, political theory, and the history of Western thought.

Augustine was born on November 13, 354, to Patricius, a pagan Roman official, and Monica, a devout Christian. He studied rhetoric in Carthage and later taught in Rome and Milan. In his youth he adhered to Manichaeism for approximately nine years before being drawn to Neoplatonism and then to Christianity. He was baptized in Milan in 387 AD, by Ambrose according to traditional accounts. Returning to North Africa, he established a monastic community and was subsequently pressed into clerical service by the congregation at Hippo. He was consecrated co-bishop of Hippo Regius around 395 AD, becoming sole bishop shortly after, and held that office until his death on August 28, 430, as the Vandals besieged the city. A fuller account of his life appears on the Augustine of Hippo - History page.

Augustine's literary output was vast. His best-known works include:

• Confessions (c. 397–400 AD) — An autobiographical account of his spiritual journey, written as a sustained address to God; widely regarded as one of the first works in the genre of autobiography.
• The City of God (c. 413–426 AD) — A large-scale work in political theology written in the aftermath of the sack of Rome (410 AD), contrasting the earthly city with the City of God.
• On the Trinity (c. 400–416 AD) — A systematic theological exposition of the doctrine of the Trinity.
• On Free Choice of the Will (c. 387–395 AD) — A dialogue examining the relationship between free will, evil, and divine foreknowledge.

He also produced extensive biblical commentaries, sermons, and polemical works against Manichaeism, Donatism, and Pelagianism.

Augustine developed positions on a range of theological and philosophical questions that became foundational for subsequent Western thought.

Original Sin: Augustine formulated the doctrine of original sin as it came to be understood in the Western church — the inheritance of Adam's guilt and corrupted nature by all humanity. This doctrine is contested among Christian denominations and is examined on the Augustine of Hippo - Original Sin Viewpoint page.

Grace and Predestination: Augustine argued that human will is bound by sin and that salvation depends entirely on divine grace, not human merit. His mature position approached what would later be called predestination. This teaching generated controversy in his own lifetime and remains disputed; see the Augustine of Hippo - Grace and Predestination Viewpoint page.

Free Will: Augustine's treatment of free will evolved across his career, moving from a more libertarian account in early works toward a compatibilist or deterministic framing in his anti-Pelagian writings. Competing interpretations are addressed on the Augustine of Hippo - Free Will Viewpoint page.

Just War: Augustine articulated one of the earliest systematic accounts of just war theory in the Christian tradition, arguing that war could be morally permissible under defined conditions. This framework is discussed on the Augustine of Hippo - Just War Viewpoint page.

Church and State: His two-cities framework in The City of God has been interpreted to support both clerical supremacy over civil authority and the independence of the temporal order. The range of interpretations is covered on the Augustine of Hippo - Church and State Viewpoint page.

Augustine drew heavily on Neoplatonism, particularly the thought of Plotinus, integrating it with Christian doctrine. He is often credited with transmitting and Christianizing key elements of Platonic philosophy into medieval European thought. His epistemology — centered on divine illumination as the source of certain knowledge — influenced scholastic debates about faith and reason. His treatment of time in Confessions (Book XI) remains a reference point in philosophy of time. His relationship to classical philosophy and its implications are examined on the Augustine of Hippo - Faith and Reason Viewpoint page.

Augustine's writings shaped Roman Catholic theology, Protestant soteriology, and medieval political thought across more than a millennium. His anti-Pelagian writings were later invoked extensively by Protestant Reformers, including Luther and Calvin, who regarded him as a forerunner of Reformation soteriology. His political theology influenced medieval debates over papal authority and the legitimacy of secular power. He has also been cited in debates about coercion, religious toleration, and the suppression of heresy. Critical and sympathetic assessments of his legacy appear on the Augustine of Hippo - Legacy Viewpoint page.

Several aspects of Augustine's thought and conduct remain subjects of active debate among scholars and theologians. Topics with dedicated Viewpoint pages are linked in the sections above. Additional disputed areas — including his views on sex and embodiment, his relationship to antisemitism in patristic thought, his influence on Western attitudes toward sexuality and gender, and the accuracy of his self-portrayal in Confessions — are candidates for future Viewpoint pages.

• Heliocentrism — A related case study in the relationship between church authority and intellectual inquiry