The title of this book is somewhat misleading. Rather than a study simply of the correspondence of the famous bishop and canonist Ivo (c 1040–1115), it is a re-evaluation of all the major works attributed to that pivotal figure in the development of mediaeval canon law. After a brief biographical survey, Rolker presents the state of canon law before Ivo and then reviews the collections either known to or compiled by the bishop of Chartres. Ivo's letters are not subject to direct consideration until almost halfway through this book, and then only selected ones are studied as they shed light on the sources of the other works.

The author presents a painstaking and detailed study of the sources and the inter-relationship of the principal works attributed to Ivo: the Tripartita, Decretum, Panormia and Prologus. Only the last of these has been universally accepted as the work of Ivo, but even here it is not clear which work it is intended as a prologue to: it has been attached to both the Decretum and the Panormia (as well as being transmitted by itself). Rolker concludes that Ivo compiled and used the massive Decretum (17 books in length) and wrote the Prologus as an introduction to this work, while Ivo probably did not compile the Panormia. The consensus of most recent scholarship, following Paul Fournier, has been the reverse, but Rolker, drawing particularly on the ongoing research of Martin Brett and Bruce Brasington, identifies Ivonian characteristics in the Decretum which are not only missing from the Panormia, but are actually contrary to what is found in this shorter work. Having said that, however, it proves impossible to come up either with a definite author or a clear date for the composition of the Panormia (the traditional date of 1095 appears far too early to Rolker, and he argues for a compilation c 1115).

Of greatest interest to someone who is not primarily interested in the text, sources and transmission of these works are the two central chapters on Ivo's views on divine law and ecclesiastical hierarchy and on marriage (principally in the long and complicated affair of Philip I's marriages to Bertha of Holland and Bertrada of Montfort). It is here that Ivo's letters are most valuable, as they show the bishop actually at work, drawing from the various collections available to him and applying the law to specific situations.

Rolker does a good job in noting the difference between Ivo's collection of canon law, building on the Decretum of Burchard of Worms, and the collections that were to follow a generation later in the Concordia discordantium canonum of Gratian. While Gratian's work (prescinding from any consideration of how many versions or authors there may have been) contained not only dicta, or comments by the compiler, but also sought to harmonise the various points of apparent conflict in the various sources. Ivo, on the other hand, lists the legal sources in his Decretum without any obvious attempt to synthesise. Ivo presents the legal sources, in all their messiness and contradiction, and leaves it to the reader and practitioner to apply the law to the facts. His correspondence vividly shows him making just such application himself.

This is not to say that Ivo abandons his reader without any principles. The primary principle is that of the salvation of souls, manifest in charity and refined by the constant antithesis (or interplay) between justice and mercy. Rolker quite explicitly plays down Ivo's connection to the growth of scholasticism (as he also clearly finds unconvincing the traditional association of Ivo with the Gregorian programme of papal reform), but it is clear that some of the characteristic forms of later scholastic method find parallels in Ivo's work. Rolker also highlights Ivo's concern with the sacraments, and points out how closely this was related to the bishop's canonical work. While Burchard's Decretum, a main source for Ivo's work, begins with a book on the ecclesiastical hierarchy in general, and papal primacy in particular, Ivo's Decretum begins with the sacraments of the faith and does not get to what appeared first in Burchard's scheme until Book V, after four books on baptism and confirmation, the Eucharist, churches and fasting. Ivo of Chartres is listed as one of the fontes for the final canon of the present Code of Canon Law in its assertion salus animarum suprema lex, and it is clear why.

This book is based on Rolker's 2006 Cambridge University PhD thesis, and contains as an appendix a lengthy concordance table for the quotations from the four ‘Ivonian’ canonical collections in Ivo's letters. As is only to be expected, Rolker's book raises more questions than it answers, and its conclusions will not meet with universal agreement as they overturn so many of the points of modern scholarly consensus. But Rolker does clearly give the state of the question on Ivo's canonical works, provides a fuller context for these works, and shines a brighter light on these sources, and it is in just this way that Ivo's letters prove most valuable.