This excellent, erudite book has both a narrow focus and a wide scope. Much about Gratian and the Decretum associated with his name is tantalisingly uncertain, in particular the Tractatus de penitentia (C 33 q 3) within that fundamental text. In Part I, Larson's focus is on the contents of the Tractatus and other related texts; Part II then broadens the scope to the reception of the treatise from 1140 to 1215. Larson makes the welcome announcement that she is preparing a new edition with an English translation of the treatise.

While Distinctio 1 has not been neglected in scholarly debates, we in fact now have the first comprehensive consideration of Gratian's Tractatus, related to Gratian's work as a whole and to its vital contribution to later developments in law, theology and practice. Larson well expresses part of the aim of Part II in stating that the study of the reception of a theological treatise embedded in a textbook filled with canons by a wide range of thinkers provides an opportunity to re-evaluate the nature and interrelationship of canon law and theology in the period covered. Although the footnotes alone – numerous and often substantial – indicate the high level of scholarship deployed, Larson can also present matters in an engaging way, as when the discussion of Distinctio 2 is headed ‘Regaining love like David or losing love like Satan’.

Interspersed in the volume are various observations on how we might gain valuable biographical information on Gratian and the nature of his formation and intentions. Larson sides firmly with those who maintain that Gratian was a teacher and the Decretum a teaching text. In terms of modern categories, Gratian taught canon law and, to a certain extent, theology, which, based on De penitentia, was mainly sacramental and pastoral in focus. Gratian believed that, while wilful ignorance is harmful to everyone, it is dangerous for priests.

Part II of this work has a fascination all of its own as it traces aspects of the great attention paid to Gratian's treatise, beginning with Peter Lombard's use of it, through its place in the classroom and outside, and finally to its reception by popes and the Roman curia. The chapter on De penitentia beyond the classroom examines the evidence from England and southern France between 1160 and 1190, and includes works by Bartholomew, Bishop of Exeter, and Master Vacarius. Larson moves with due caution, as in remarking of one of Alexander III's letters that a specific section of the treatise can be identified as the intellectual source of the decision, while in other decretals the work of Alexander's curia was guided by more general principles and ideas present in Gratian's treatment of penance and governing his approach to practical issues of penance.