MS Vatican BAV, Barb. lot. 3589 has been known to scholars since the nineteenth century, but has never been thoroughly studied. This article investigates its contents and its composition, identifying its texts and, so far as possible, their sources, while searching for clues concerning the compiler's background and manner of working. The codex has proved to be an outstanding document for the study of medieval magic for many reasons. It brings to light previously unnoticed works, such as the remarkable Libre de puritats, and provides a rare sampling of necromancy in a Romance language - Occitan - interacting with Latin. It also constitutes a new witness, although incomplete, for writings about occult arts known through other Latin manuscripts, in particular the Liber septan planetarum ex scientia Abel, the De officiis spirituum and perhaps the Liber Veneris. In addition, the codex shows evidence of the use of fundamental manuals of magic, such as Liber Razielis and Pieatrix, whose medieval circulation is not well known, and gives the tides of many lost works and information about their contents. Last but not least, it offers a window on the way in which an early fifteenth-century necromancer formed his own collection of magic books and resources. © BREPOLS & PUBLISHERS.