An academic work analyzing religious movements that emphasized direct, emotional, and charismatic experience (enthusiasm) over formal doctrine, particularly in the 17th and 18th centuries. The author defines enthusiasm not as ordinary fervor, but as a tendency toward 'ultrasupernaturalism'. This is a view in which adherents expect more tangible and immediate results of God's grace in their daily lives, often going beyond the teachings of the mainstream church. The book examines various movements considered 'enthusiastic' or deviant from orthodoxy, such as the Quakers, Jansenism, Quietism, Methodism, Montanism, Donatism, and the Anabaptists. In 23 chapters, the author traces the historical roots of these movements from the early church to the 18th century, highlighting how they often emerged as a reaction to perceived cold religious formalism. As a Catholic theologian, he provides a critical analysis while also sympathetic to the deep longing of these movements for intimacy with God. This book examines how enthusiasm movements often begin with a fiery (charismatic) zeal but tend to fade or transform into established institutions over time. It is considered a classic study of the charismatic religious phenomenon in Western Christian history.