This work deals with the theological and medical critique of enthusiasm in the 17th and early 18th centuries and with the relationship between enthusiasm and the new natural philosophy in that period. Enthusiasm at that time was a label ascribed to various individuals and groups who claimed to have direct divine inspiration - prophets, millenarists and alchemists as well as experimental philosophers and even philosophers like Descartes. This book attempts to combine the perspectives of intellectual history, Church history, history of medicine and history of science in analyzing the various reactions to enthusiasm. The central thesis of the book is that the reaction to enthusiasm, especially in the Protestant world, may provide an important key to the origins of the Enlightenment and to the processes of secularization of European consciousness.