Exorcism, the persecution of witches and conversations with demons, are not medieval practices, but can, and in an extensive form, be found in the early modern period. Philipp Stenzig's thesis is that these practices were a means in the age of the Reformation, i.e. in the late sixteenth and early seventeenth century, to on the one hand test an individual's confessional position, and on the other hand to discipline people and society. The sources for this thesis are broadly quoted and consist mainly of handbooks for exorcists and reports of interrogations of those suspected of dealings with the devil. The author does not deal with the liturgical aspects of exorcism, nor with its theology, but with the rationality of these trials, since they were seen as a means of obtaining more knowledge about the hidden powers of nature. Demons know more about reality than man, so those who are in touch with demons are a source for scientific knowledge, which explains the title of the book – exorcism being a school of the devil. Stenzig has given this aspect of research into the early modern period, about which there exist many popular misunderstandings, an interesting, interdisciplinary approach.