Gnosis ("knowledge") is among the most fascinating phenomena in the history of religions. Its direct parallels with the modern Esotericism has intensified significantly in recent times, interest in this ancient form of religion. This book is a complete and updated the status of research on Gnosis, and shows clearly where the certainties end and assumptions begin as dark on this phenomenon in the history of religion. Its author, Christoph Markschies, is one of the youngest professors of ancient history of the Church. This book describes the main sources Markschies ancient authors both critics and supporters of the Gnostic, to shed some light on what for some is a religion itself and for others a form of knowledge heretical. Students of history, historians, philosophers and philosophy students, theologians and all those who are interested in Gnosticism.