This volume examines developments in the churches of the East and the West in the High Middle Ages, including major Western movements such as the reform papacy, the crusades, and scholasticism, and their impact on the Eastern Church. Concurrently, the author explores the theological and spiritual tides that spread from Byzantium to the northern regions of the Balkans and Rus', and lastly recounts the stories of the native churches of Egypt, Ethiopia, Syria, Armenia, and Georgia.