During the Renaissance there was no centralized Inquisition in northern Italy until Pope Paul III founded the Roman Inquisition in 1542, but there was a dense network of autonomous papal inquisitors. Based on extensive archival research, this study investigates the life of the Dominican friars from whom these inquisitors were mostly drawn. It focuses on a selection of hitherto almost unknown but representative inquisitors to cast new light on their formation, appointment and careers, as well as their principal pursuits - the prosecution of heretics, especially Waldensians and Judaizers, and, most of all, the hunting of witches, for it was at its most intense in northern Italy during the Renaissance, over a century before reaching its peak in Northern Europe.