The publication of the Decretum of Gratian marked a fundamental step in the development of Church law: by collecting, classifying and systematising what had gone before, Gratian established a structure that led directly to the Code which rules the life of the Catholic Church today. Adam Vetulani was early recognised as an outstanding scholar of canon law, and this volume presents a selection of studies which bear directly upon the Decretum and upon the decretists and collections of decretals most closely related to it, together with a substantial section of Addenda. A subsequent volume will contain articles on other canonists and on the institutions of the medieval Church. Vetulani's mastery of the subject and his attention to detail - and the fact that he drew upon previously unexploited materials, notably from the libraries of Poland - have ensured that his work remains of fundamental importance. Between them, these articles deal with the circumstances of the Decretum's composition and propogation, and with its purposes, and they aim to determine what was the original form of the Decretum and what may be attributed to subsequent elaborations and accretions. In this context Vetulani's analysis of the place of Roman law in Gratian's work has proved especially fruitful. L’arrivée du Décret de Gratien marqua un pas majeur dans le développement du droit de l’Eglise. Ce volume presente une sélection des études d’Adam Vetulani sur le Décret, ainsi que sur les décrétistes et les collections de décrétales s’y rapportant de façon proche. Le tout est accompagné d’une section d’addenda de poids. Le recueil suivant contient une serie d’articles sur d’autres canonistes et sur les institutions de l’Eglise médiévale. Adam Vetulani, dont l’extraodinaire érudition en matière de droit canon fut très rapidement reconnue, fait prevue d’une grande maîtrise du sujet. Son oeil pour le détail - et le fait d’avoir trouve ses sources dans les do