In this work, Loewen investigates thirteenth-century Franciscan thought on music, reserving the subject of Franciscan musical practice for a later work. He casts his net wide, refusing to limit himself to those passages within Franciscan literature specifically dedicated to music. Thus he begins with a section on Francis which does a good job of teasing out what can be said about Franciscan thought on music from studying early hagiographic writings and art concerning Francis himself. In his consequent analysis of writings by William of Middleton, David of Augsburg, Robert Grosseteste (an honorary Franciscan, so to speak), Roger Bacon, Bartholomaeus Anglicus and Juan Gil de Zamora he looks at the total body of their writing, placing what each said about music within the context of their thought as a whole. He is sensitive to the Aristotelian, Augustinian and Boethian roots of western music theory, and, more directly, to the significance of Lotario dei Conti Di Segni's (i.e., the future Pope Innocent iii's) De missarum mysteriis, which, Loewen says, ‘would supply the Franciscans with the essential building materials to restore the Roman church musically’. Loewen stresses that as Pope Innocent iii Lotario would approve ‘the Franciscan way of life leading to the corollary of music and penitential preaching, … two important themes in De missarum mysteriis'. Indeed, the relevance of Franciscans' understanding of music to their preaching ministry could be seen as the major subject of this book, and Loewen pursues it in a manner that is complex but remarkably informative. If the success of a book is measured by its ability to make the (presumably well-informed) reviewer see a subject through new eyes, then this thoroughly interdisciplinary work can be considered a success.