Monica Azzolini takes the reader on a fascinating journey through Renaissance Milan, showing in its social and political context the various roles astrology played at the court of the Sforza during the last decades of the fifteenth century. The aim of the work is initially presented as being to focus on the political uses of astrology in the specific context of this court, considering the presence near the ducal family of astrologers and physician–astrologers trained at the University of Pavia. The author accomplishes this goal, and goes beyond it by displaying a rich network of relationships of practitioners of astrology with members of the court, based on knowledge, patronage and personal influence; she also presents a study of the discipline, as found in the university context, and of the practice of medical astrology at court.

Each of the chapters is constructed differently, drawing information from sources of different kinds, but creating a succession of well-connected sections culminating in the last one – in which the argument of the book, that astrology played a bigger role in politics during the Renaissance than is usually accepted, virtually blazes before the eyes of the reader.

A first step is a reconstruction of what Azzolini calls a corpus astrologicum, the likely content of the curriculum of astrological studies at the University of Pavia and probably other Italian universities during the fifteenth century. Starting with a manuscript student's notebook, and combining it with personal inventories of the libraries of university professors, with a study of scientific book printing of the period, and with the information available on the Ducal Library at Pavia, she re-creates that body of knowledge which would be put into practice at the ducal court.

The following chapters go through the various periods traversed by the Duchy of Milan, as determined by its rulers, from the last Visconti to Ludovico ‘il Moro’. Each chapter is built around the different uses they made of astrology. The limited interest in astrology of Francesco Sforza (duke from 1450 to 1466) is of use for presenting the kind of astrological advice (sometimes unsolicited) that a Renaissance ruler received, and contextualizing the search for patronage of astrologers and the utility of prognostications intended to establish, and to some extent control, public opinion. Through consideration of his wife Bianca Maria Visconti and her interest in promotion of the court physician–astrologer at the university, this second chapter also shows the links between both worlds, as well as the techniques of active patronage.

Galeazzo Maria Sforza (duke from 1466 to 1476) is presented in the third chapter as a patron intensely interested in the various applications of astrology for personal and political goals. Based on letters and diplomatic documents, the chapter introduces the use of astrological prognostications in creating political rumours that could affect the diplomatic policies of rival and allied states. Azzolini describes also the role of natal charts in political decision making and in the arrangement of marriages, considering the relationships of the Milanese court with the Gonzaga court in Mantua and with the court of the Este in Ferrara, and above all the rivalry with the kingdom of Naples and Ferrante of Aragon.

The focus of the chapter dedicated to Gian Galeazzo Sforza (duke from 1576 to 1494) is medical astrology. A complex web of correspondence involving Gian Galeazzo, his wife Isabella of Aragon and his physicians and assistants with his uncle Ludovico (the actual ruler of the duchy) is analysed, allowing the author a rich description of the kind of astrological medicine practised at the castle of Pavia with the young duke. The way the physicians used astrology to explain the sickness, to decide the right moment for treatments and to formulate a prognosis emerges clearly through Azzolini's words. There is a strong emphasis in this chapter on the theory of critical days, which seem to obscure other medical–astrological theories and practices somewhat; however, it is apparent that this is what the sources themselves show.

The final chapter brilliantly rounds off the work, focusing on Ludovico Sforza, ‘il Moro’ (officially duke from 1494 to 1499). His reliance on astrology led him to trust one specific practitioner, taking his advice not only for marriage arrangements and medical issues, or for politics, in the way his predecessors had done. The letters and astrological charts studied show how, going further, he used astrological interrogations and elections (branches of the astrological practice considered out of the realm of natural astrology and thus not generally accepted as legitimate) for choosing the right moment for travelling, for initiating battles in war, and for undertaking diplomatic activities.

One of the strengths of the book is that it avoids simplifications about Renaissance astrology, as well as about Renaissance medicine, politics and patronage systems. The Duke and the Stars also constitutes an impressive example of how archival research, and the use of varied sources, including archive documentation, can not only enrich, but also change, the understanding of Renaissance court science and politics. That studies on astrology are currently part of studies of science and society during the Renaissance and the early modern period is true; that the dismissal of studies of the ‘occult sciences’ (the once ‘wretched’ subjects) from the history of science has already been amended should also be considered beyond doubt. The publication of several works in the last few years attests to this. However, there is still need for systematic, deep, serious studies on many themes, such as what kind of astrology was part of the training at the universities in different periods and contexts, the role of astrologers at many European courts, and the practices of medical astrology as applied in everyday life. Monica Azzolini's remarkable work contributes to current scholarship in such a way, creating a picture of interest for anyone concerned with Renaissance political, cultural and intellectual life.