This volume examines the way the Belgian historian of religions Franz Cumont (1868–1947) and his contemporaries conceived of early Christianity's relation to the ancient mystery cults. As the comparative study of religion rose to academic prominence in late 19th century Europe, this question provoked fiery debates, fuelling methodological, ideological, and religious divides between scholars of different scientific and personal backgrounds. Cumont was a worldwide authority in the scientific study of the religions orientales, but he expressed his opinion on their relation to Christianity only ambiguously. Yet, his publications deeply impacted the debates of his time because of the numerous similarities they revealed between Christian and pagan traditions. Written by specialists from various academic disciplines (e.g., history of religions, theology, New Testament studies), this collection of papers offers a much-needed study of how Cumont and other leading 19th century scholars discussed this theme. It also offers critical reflections on what is left of their ideas in present-day research on this most fascinating subject matter in the study of ancient religion.