This book investigates the nature and origins of Gnosticism, a complex religious and philosophical movement that influenced early Christianity. G. R. S. Mead, writing before the significant Nag Hammadi discoveries, synthesizes the available knowledge of Gnosticism from the turn of the twentieth century. He critically examines sources from both the Early Church Fathers, who were often hostile to Gnosticism, and the limited corpus of actual Gnostic documents accessible at the time. The work aims to provide a comprehensive understanding of Gnostic beliefs and their historical context.

This work is regarded as a foundational text for understanding Gnosticism, particularly for its insights into the state of knowledge before the Nag Hammadi discoveries. Mead's meticulous approach, drawing from both adversarial and primary sources, provides a comprehensive overview of what was known about Gnosticism at the turn of the 20th century. It is frequently recommended for students of early Christianity and esoteric traditions. The book's detailed summaries and manuscript excerpts offer significant value for scholarly research.