Popular religion, along with the wider field of popular culture, has only been a recognized subject for historical investigation for a relatively short time; the bibliography is virtually non-existent before 1970. Even so, a term that was at first accepted as comprehensible and useful has rapidly come to be seen as highly problematic. Among the multiple reasons for concern, two in particular stand out. Historians now recoil from any suggestion that there was a single or coherent phenomenon that could be labelled in this way, while detailed research has largely destroyed the notion of a clear frontier between “official” and “popular” beliefs and practices. These discussions have been particularly lively in the case of France, where the nature of religious change under the Ancien Régime raises important issues with wide relevance, and the documentation is unusually rich.