The book contains polemical works directed against the Monophysites and written by Orthodox Chalcedonites: Leontius of Jerusalem (VI-VII centuries) and Theodore Abu-Kurra (VIII-IX centuries), as well as a dogmatic-hereseological treatise by Leontius, a Byzantine scholastic ( second half of the 6th century) “On sects.” The publication of these works, translated into Russian for the first time (Abu-Kurra’s treatise is also translated into a modern European language for the first time), significantly clarifies and expands the understanding of Russian readers about the nature and essence of the polemics with the Monophysites and some other heretics on issues of Christology and church history, both in The Byzantine Empire, and beyond. The book is intended for theologians, philosophers, historians and everyone interested in the fate of the Church.