It is the opinio communis of modern scholarship that in the years 1093–5 Bishop Ivo of Chartres (1090–1115) composed three comprehensive collections of canon law, the Collectio tripartita, the Decretum and the Panormia, as well as a treatise on the foundations of ecclesiastical law, often transmitted as the preface to the Decretum or Panormia, and known as Ivo's Prologue. On this view the first two parts of the Collectio tripartita, containing chronologically ordered excerpts from papal letters and councils, were intended as a preparation for the Decretum, and the Panormia was Ivo's user-friendly revision of the Decretum, difficult to use with its over 3,700 canons. The Panormia is to be viewed as Ivo's most important work – the Prologue was in fact written for it, and the wide manuscript distribution of the Panormia confirms the correctness of this view. The Decretum, on the other hand, represents a preliminary and less well-thought-through source collection. The examination of this general view is the subject of the book under review, originally written as a thesis under Martin Brett in Cambridge. For that the attribution of all these works to the bishop of Chartres rests upon hypotheses, even if these came into being in the twelfth century, is shown by the fact that none of the collections in question, not even the Prologue, names Ivo of Chartres as the author. Rolker divides his study into eight parts, of which the first three introduce the subject. The first chapter (pp. 1–49) sketches the activity of Ivo as abbot in Beauvais and his conflict-ridden time as bishop of Chartres, as well as the long history of research, mainly devoted to the changing attribution of the canonical collections to Ivo, whose current elements have been outlined above. In the second chapter (pp. 50–88) Rolker introduces canon law collections which were known in the eleventh century in northern France, the Decretum of Bishop Burchard of Worms from the beginning of the eleventh century having played the most significant role as a model for these new collections. This is followed by an examination of the sources and models which Ivo of Chartres made use of in the collections of canon law attributed to him. These were Burchard's Decretum, the Pseudo-Isidorean Decretals, the Collectio Britannica, as well as a body of smaller collections, which were drawn upon for the Collectio tripartita A, the Decretum and Ivo's Prologue. On the other hand the Panormia, which largely depends on the Decretum, makes no direct use of these sources, but adds new canons from the Collection in Four Books and from a further collection, partially transmitted in Paris, Bibliotheque de l'Arsenal, ms 713, which are not used in the other collections attributed to Ivo. This discovery makes the generally accepted view that all four canonistic works were composed by Ivo within a the space of a few years improbable. In order to examine this problem from a more solid foundation, Rolker's fourth chapter analyses the sources of the numerous canonical quotations in the extensive and widely disseminated collection of Ivo's letters. The detailed evidence for this investigation is given in a substantial appendix (pp. 303–38), listing the parallels between the quotations in Ivo's letters and the collections attributed to him, Tripartita A and B, Decretum and Panormia. Rolker concludes that Ivo drew widely on the Decretum throughout his letters and that this collection already existed as an independent work by around the year 1094. The use of the Collectio tripartita can also be demonstrated, though there are no indications that Ivo was its author. On the other hand the letters show no evidence of the use of the Panormia. These source-critical examinations are supported by an equally intensive treatment of the question of the nature of Ivo's conception of ecclesiastical law, what type of theology lay at the root of his understanding of law, and whether this conception is reflected in the collections attributed to him (chapters v–vii). Chapter v concerns itself with Ivo's understanding of law and his basic theological ideas, which are defined in the first instance from his programmatic Prologue, the Decretum and from his letters. Here the author is able to show impressively that for Ivo his work as a pastor of souls was paramount, deriving from an idea of the primacy of the community of believers close to that of Augustine. The most important commandment for the Church has to be the saving of the sinner; in accordance with this maxim the law is to be applied in full (rigor canonum) or according to the dictates of mercy (misericordia), where preference is given to mercy. Against that, the Church as a corporate and hierarchically and legally organised institution is given less significance. Contradictory canons are an expression of both of these principles; Ivo incorporated these contradictions in his Decretum consciously, leaving the user the possibility of a free decision. These principles are the leading ideas in the Decretum, which begins deliberately with sacramental doctrine and ecclesiology, only moving on to deal with ecclesiastical hierarchy in book v, in contrast to the Decretum of Burchard of Worms, its most important source, which opens with the hierarchical structure of the Church. This makes it easy to explain Ivo's lack of interest in a discussion of the relative weight of different types of source, for what mattered was whether the canons asserted mutable or immutable law. As an example of the practical implementation of these opinions, the sixth chapter is taken up with Ivo's understanding of marital law, on which he incorporated important new texts in his Decretum. The following chapter returns again to a comparison of the Decretum and the Panormia (pp. 248–89), discussing the differences in the character of these collections, their reception and the dates of their compilation. While in the Prologue, Decretum and the letters of Ivo the work of the priest and of the judge is articulated as a balancing act between mercy and legal stringency, the Panormia, by contrast, more obviously attempts to eliminate contradictory canons, or to harmonise them, and to offer a solution according to scholastic method. The claim for a narrow reception of the Decretum, limited to Chartres, is convincingly refuted. The work was available by 1094, and the Prologue, incorporated in the earliest collections of Ivo's letters, was already circulating by 1105, while there is no evidence for use of the Panormia before 1115. This leads to the conclusion that it is as wrong to claim that Ivo is the author of the Panormia, and thought of it as his own distinctive work, as it is to hold that the Prologue was actually written for this collection. It is much more appropriate to the Decretum, even if one has to take account of the possibility that it was originally Ivo's independent treatise. The close parallels in conception and use of sources between the letters of Ivo, the Decretum and the Prologue reinforce the view that only the Decretum should be considered Ivo's canonical work. The last section of the book examines Ivo's role in canon law more closely, rejecting the proposition that the bishop of Chartres was the forerunner of the scholastic method, linking canon law of the period of reform with the scholasticism of the twelfth century. Ivo is much more to be seen as distinctively individual, with a conception of law derived from his theology, his understanding of the sacraments and his work as a pastor. The mandatory index of manuscripts, sources, quoted letters of Ivo, persons, places and subjects conclude this excellent study, from which all future work on the ecclesiastical law and theology of Ivo of Chartres will have to begin.