The book deals with the policy of the Byzantine state in the field of ecclesiastical matters from the end of Iconoclasm in 843 to the death of Emperor Basil I in 886. It examines the attitude of the main political actors – the emperors and their closest collaborators – towards religious matters and the decisions they made concerning the various issues of Iconoclasm and Orthodoxy, appointment of the patriarchs, relations with the Church of Rome, and theological disputes with Muslims, non-Chalcedonian Christians, and Christian sects. This volume also considers missionary activity outside the borders of the Empire and policy towards religious minorities inside them, as well as the political and intellectual potential behind it.