John Damascene, one-time senior civil servant in the Umayyad Arab Empire, became a monk near Jerusalem in the early years of the eighth century. He never set foot in the Byzantine Empire, yet his influence on Byzantine theology was ultimately determinative, and beyond that his theological work became a key resource for Western theology from Scholasticism to Romanticism. His searching criticism of Imperial Byzantine iconoclasm earned him harsh condemnation from the Byzantine iconoclasts. This is the first book to present an overall account of John's life and work; it makes use of recent scholarship about the transformation of the former Byzantine territories of the Middle East after the seventh-century Arab Conquest, and the new critical edition of the Damascene's prose works. It sets John's theological work in the context of the process of preserving, defining, defending, and also celebrating the Christian faith of the early synods of the Church that took place in the Palestinian monasteries during the first century of Arab rule. John's own contribution is explored in detail: his amazing three-part Fountain Head of Knowledge, which provided the logical tools for arguing theologically, outlined the multifarious forms of heresy, and set out with clarity and learning the fundamental doctrines of Orthodox Christianity; as well as his treatises against iconoclasm, his preaching, for which he was famous in his lifetime, and, the work for which he is most renowned in the Orthodox world, his sacred poetry that still graces the liturgy of the Orthodox Church. The life and thought of this subject of the Arab Caliphs, a Christian monk who thought of himself as a Byzantine, poses intriguing questions about identity in a rapidly changing world, and the deeply traditional nature of his presentation of Christian theology calls for reflection about the relationship between tradition and originality in theology.