The Gnostic Trilogy is the best-known and most important work by the ascetic philosopher and teacher Evagrius of Pontus. Among the writers of his age, Evagrius stands out for his short, perplexing, and absorbing aphorisms, which provide sharp insight into philosophy, Scripture, human nature, and the natural world. The first part of the trilogy, the Praktikos (The Practiced One), provides a diagnosis and treatment of the eight tempting thoughts. It was a foundational text for monastic asceticism and was the basis for the later Seven Deadly sins tradition. The second, Gnostikos (The Knower), explains how someone who has mastered the body and mental delusions should teach others. The third, longest, and most controversial, the Kephalaia gnostika (Gnostic Chapters), ranges broadly over the origin of the universe, the nature of rational beings, and the hidden symbols of Scripture. This part was responsible for Evagrius's condemnation as a heretic and, as a result, does not survive intact in the original Greek and must be restored from ancient translations. This volume presents the Trilogy in its entirety for the first time since antiquity and provides a fresh, comprehensive English translation of all three works, in all their known ancient versions, both Greek and Syriac. Detailed explanatory notes, cross-references to Scripture, to ancient literature, and to Evagrius's other writings, as well as commentary on the translation techniques of the Syriac translators, provide the necessary resources for understanding this significant but puzzling text.