This book is concerned with the ways in which the radical fourteenth-century political thinker Marsilius of Padua used and interpreted Aristotelian concepts and terms in constructing his own arguments. This line of enquiry is in itself not a new one: Marsilius' use of Aristotle has been a staple of treatments of his works. But Vasileios Syros has succeeded in providing the greatest treatment in depth of these issues so far. He has revealed in profound detail how far Marsilius followed Aristotle's ideas but, more important, how far he diverged from them. In particular, Syros shows clearly how consent played a systemic role in Marsilius' political theory, in a way which was alien to Aristotle's approach. Similarly Marsilius' notion of the human legislator was very different from Aristotle's use of the term ‘legislator’. Syros also reveals the extent to which Marsilius is willing to incorporate the vulgus into the political community in a way that Aristotle was not. These are just a few of the important issues addressed. But I wonder whether the scope of the book is too narrow. It is only concerned with the first discourse of the Defensor pacis. This is, of course, where the bulk of references to Aristotle are to be found. But to focus solely on this part of the work distorts interpretation of Marsilius and perpetuates the out-moded approach of some political scientists who treat only this section. I can see why Syros has made this decision but readers of Marsilius should be aware (especially in the light of the recent publications of Annabel Brett and George Garnett) that the whole spread of Marsilius' work has to be taken into account, especially the second discourse of the Defensor pacis. One line of enquiry which Syros has opened up further is that of the Jewish and Islamic origins of Marsilius' ideas: in particular his treatment of the works of Maimonides as a source for Marsilius' notion of transient acts is illuminating. Also of particular note is Syros's discussion of Albertus Magnus as a source for the elaboration of Marsilius' key notion of law as a coercive precept. Syros has written a highly useful book which will help both scholars of late medieval political thought and also those concerned with the transmission of Aristotelian ideas in this period.