The Flemish Jesuit scholar Martin Delrio (1551–1609) is mainly known to historians for his encyclopedic, three-volume work on demonology, the Disquisitionum magicae, published in 1599–1600. This intellectual biography by Jan Machielsen has its own encyclopedic ambitions, reconstructing the whole of Delrio's scholarly career in detail and placing the Disquisitionum in context. A committed Counter-Reformation zealot, Delrio briefly served Don John of Austria as a lawyer before entering the Jesuit order. The Jesuits encouraged his early interest in humanism; their educational ambitions called for research on everything, not just Catholic evangelism. Delrio edited Seneca's plays, with extensive commentary that helped to solve problems of authorship, but already displayed the tendencies towards wheel re-invention and kitchen-sink inclusion that would characterise the Disquisitionum.

Unusually for a demonologist, Delrio seems never to have met a witch in person, but, when he turned to witchcraft, his Seneca edition had given him intimate acquaintance with the classical sorceress Medea. In the fifteenth century, early demonologists had regarded witches as a ‘new sect’ of heretics, but by Delrio's time it was conventional to assert that witchcraft and magic were to be found in all times and all places. To compile the Disquisitionum, Delrio ransacked saints' Lives, histories of everywhere from Scandinavia to Peru and China, and of course the classical poets, all of whose works he regarded as basically true. Machielsen explains Delrio's research methods in the context of Jesuit note-taking practices. He also shows why his work was such a success in its day. Later ages would see Delrio as ‘credulous’ and ‘uncritical’ in his approach to sources, but he saw himself as faithful to his texts in true Renaissance style. And, while he naturally disclaimed originality, he presented himself as the first scholar to have approached the subjects of magic and witchcraft from the three disciplines of law, philosophy and theology. In this he was perhaps unfair to his predecessor Jean Bodin, whose Démonomanie of 1580 had already done this and was arguably more original in its time. Still, Delrio's work, like Bodin's, was a huge publishing success, and remained in print longer than any other demonological work, last being issued in 1755. Machielsen's book can be recommended, not just as a study of ‘demonology’, but as a reconstruction of the broader concerns of a scholarly Jesuit.