This is the first modern study in English of the life and thought of the ninth-century Byzantine theologian and monastic reformer, Theodore the Stoudite. Cholij provides a complete analysis of and guide to all the primary source material attributed to Theodore. If the monastic leader is considered in the context of the tradition to which he belonged, it is clear that his religious formation occurred within a widely established school of Basilian and Palestinian Christian thought. This encourages a fresh engagement with the subtleties in Theodore's behaviour towards the Byzantine religious and secular leaders of his time and provokes new conclusions concerning the religious and secular issues which involved Theodore in controversy. Cholij refutes the established view of Theodore as a breaker of the traditional Byzantine church and state relationship and provides new insights into Theodore's true understanding of the involvement of the Emperor in church affairs. In his analysis of the rites of holiness that belonged to Theodore's church, the author identifies a false tradition of sacramental mysteries in a misreading of Pseudo-Dionysios the Areopagite and so offers a radically new definition of the origins of the Orthodox sacramental tradition.