This is a study about the history of ideas as it became manifest in southern German music theory in the eleventh and twelfth centuries, that is in, among others, the writings of Bern of Reichenau, Hermannus Contractus, William of Hirsau, Theoger (later bishop of Metz), Johannes (known as ‘Afflighemensis’ or ‘Cotto’), Aribo (of Freising) and Frutolf of Michelsberg (Bamberg). Due to the scarcity of preserved biographical background information, and their specialised character, these writings have not so far often attracted scholarly attention. (An exception is David Hiley's influential Western plainchant [1993] which devoted part of its fifth chapter to this group of writers.) The book under review does not always provide completely new information but it establishes a new, sensitive perspective by pulling together precious threads which had lain dispersed since the earlier studies of Huglo, Bischoff and others. Two main merits may be singled out here. First, the necessary historical context is (re-)created, that of the monastic reform of the tenth-eleventh centuries in southern Germany and Austria (Gorze, Hirsau). These activities, with their emphasis on the proper celebration of liturgy, obviously provided the socio-economical and cultural basis for an intensified, music-based scholarly effort in this area. Whether it is at all possible to establish tangible proof of the connection of reform-thinking and the music of reform and the treatises is a wider, more difficult question, and is not addressed in this book. Second, German medieval writing about music theory is rescued from the periphery of academic attention. The interest of these writings in definition, classification and measurement is explained as an element in and embodiment of medieval scholarly thought, on the one hand traditional, but also in touch not only with modern Guidonian music theory, but also with Aristotelian- and Platonic-influenced early scholasticism. The author's particular emphasis on the role of Hermannus Contractus as the leading eleventh-century figure in innovative German musicological thought is appropriate. Given the impressive amount of scholarship displayed in this book I miss an attempt to pinpoint any traces of a connection between these theories and composition practice (as they have indeed been demonstrated for Hermannus by David Hiley). The analytical establishment of a clearer connection between these theories and preserved contemporary music is still a desideratum. Worth mentioning is the unpretentious presentation of these quite difficult materials for the modern, non-specialised, reader, an achievement in itself. This makes the book one to recommend for use in academic teaching, while its handsome, almost bibliophile design makes it a private indulgence.