Khosrovik Targmanich was one of the greatest theologians of the Armenian Church. He lived in the 8th century and was one of the main doctors of Manazkert Council of 726 AD. In this book, the definitions of that Council are analyzed and explained in detail. Due to the clarity of mind, the five letters, comprising this book, are among the best accounts of the Christology of the Armenian Church. The original Armenian text and the English translation are presented on facing pages. The original comparative text was compiled on the basis of five manuscripts, one of which was never taken into the account for publishing the text. The English translation is published for the first time.