This book is a new edition and translation of the Nag Hammadi tractate, The Concept of Our Great Power, with introduction and commentary. It suggests that the tractate is composite, and that its basis was a non-Christian Gnostic apocalyptic work whose background may have been Samaritan, and which emanated from a breakaway Simonian group who, unlike other Simonians, believed in celibacy. The tractate later received Christian additions. The last of these may refer to the career of Julian the Apostate. This is a fresh approach to the interpretation of this puzzling tractate.