This is a study of the papacy and its relations with western Christendom in the period from the accession of Gregory VII to the death of Celestine III. In order to compress so large a subject into a relatively small book, my approach has inevitably been selective. I must, therefore, begin by explaining precisely which aspects of papal history are treated in this study. Firstly, my subject-matter is the papacy's relations with the churches and kingdoms of the west. To have included a survey of papal relations with Byzantium and the other neighbours of western Christendom would have made the book far too long and so I was obliged to omit this complex topic. The first part of my book presents the institutions of the papal government in action. Chapter one deals with the problems of governing the city of Rome and the lands of the papacy (‘the Patrimony of St Peter’). The following six chapters examine the institutions by means of which the papacy sought to govern the western Church: the college of cardinals and the curia (chapter two), the papal council (chapter three), the papal legation (chapter four), papal judicial institutions and the pope's legislative authority (chapter five), the papal protection accorded to religious houses (chapter six) and papal financial institutions (chapter seven). All these institutions were either created or remodelled to serve the needs of the reform papacy in the later eleventh century.