In a historical introduction to each period, Robert Somerville and Bruce C. Brasington discuss major developments in canon law and the individual prefaces, their authors and settings, and their sources and major themes. Early documents reflect the world of the monastic and cathedral school, when compilers attempted to fashion collections of laws that were both faithful to older tradition and suitable for the needs of their local churches. In prefaces to eleventh - and twelfth-century collections, the impact of ecclesiastical reform becomes apparent. Compilers sought to work out a systematic jurisprudence of canon law during the Investiture Contest, as church and secular authority clashed. Prefaces from the twelfth century and later express the professional legal culture of the High Middle Ages: lawyers trained in the environment of both university and papal curia undertook systematic commentary on canon law, employing terms and techniques from the revived study of Roman law.