For those living in the East Roman Empire, it was God-protected, immune from the impermanence of other states. But in late Byzantium, intellectuals began to reconsider this assumption: could the East Roman Empire be vulnerable, even temporary? And what would that mean for the Orthodox Church? Through his engagement with influential intellectuals at the time, principally Philotheos Kokkinos, Demetrios Kydones, Cardinals Bessarion and Isidore, George Gemistos Plethon, Mark Eugenikos and George Scholarios, Norman Russell explores the strategies and responses to this seismic shift in the imagination and conceptualisation of the Church and the Empire. By exploring the details of such crucial events as the Hesychast Controversy, the ecclesiastical revolution that followed, and successive attempts to attain ecclesiastical union with the West, Norman Russell considers how the Orthodox Church adapted to survive and flourish under Ottoman rule. This is an important new contribution to the scholarship of the Orthodox Church in the Byzantine period, of interest to scholars of Byzantine civilisation, the East Roman Empire, and the Orthodox Church.