For decades, Arthur D. Nock's famous definition of conversion and his distinction between conversion and adhesion have greatly influenced our understanding of individual religious transformation in the ancient world. The articles in this volume – originally presented as papers at the conference Conversion and Initiation in Antiquity (Ebeltoft, Denmark, December 2012) – aim to nuance this understanding. They do so by exploring different facets of these two phenomena in a wide range of religions in their own context and from new theoretical and empirical perspectives. The result is a compilation of many new insights into ancient initiation and conversion as well as their definitions and characteristics.