Galeotto Marzio completed the De doctrina promiscua around 1490, dedicating it to Lorenzo de’ Medici. The medical-astrological text primarily discusses topics in the domain of astrological medicine, covering issues of astronomy, pharmacy, and physiognomy in this context, but it also goes into poisons, various herbs, and talismanic magic. The treatise is mostly based on Aristotle’s natural philosophy, Galen’s physiology, and the Arabic and Paduan reception of these, which are usually linked to the work of the Persian Avicenna and professor Pietro d’Abano, a thirteenth-century physician, philosopher, and astrologer. The treatise also plays an important role in the medieval and early modern debates on astrology, since the author joins the tradition according to which astrology plays an indispensable role both in healing as well as diagnosing the outcome of an illness. The present edition is the first complete critical edition of the work, which takes into account both extant manuscripts of the text. The introductory study aims at presenting the parallels between the De doctrina promiscua and the works of the Paduan philosopher-astrologer, Pietro d’Abano, including the latter’s concept of science.