Building on critical work in biblical studies, which shows how a historically-bounded heretical tradition called Gnosticism was 'invented', this work focuses on the following stage in which it was "essentialised" into a sui generis, universal category of religion. At the same time, it shows how Gnosticism became a religious self-identifier, with a number of sizable contemporary groups identifying as Gnostics today, drawing on the same discourses. This book provides a history of this problematic category, and its relationship with scholarly and popular discourse on religion in the twentieth century. It uses a critical-historical method to show how and why Gnosis, Gnostic and Gnosticism were taken up by specific groups and individuals - practitioners and scholars - at different times. It shows how ideas about Gnosticism developed in late nineteenth- and twentieth-century scholarship, drawing from continental phenomenology, Jungian psychology and post-Holocaust theology, to be constructed as a perennial religious current based on special knowledge of the divine in a corrupt world.David G. Robertson challenges how scholars interact with the category Gnosticism, and contributes to our understanding of the complex relationship between primary sources, academics and practitioners in category formation.