Between the eleventh and twelfth centuries, the religious environment of the Pistoia area was profoundly influenced by the different currents of the ‘Gregorian Reform’, which arrived here early and strongly contributed to change the internal balance of power in the local diocese. This intervention aims to retrace the main events that occurred at this time in the religious history of Pistoia, trying to make the events of the local episcopate dialogue with those of the main ecclesiastical institutions active in the diocese, including, in particular, the rectory of San Zeno and the monastic communities most capable of carving out an important role in the spiritual, but also political, dynamics of the territory. An attempt will thus be made to highlight the factors that contributed to the success of the reform movements and, above all, to determine the particular ‘Vallombrosan’ connotation of the diocese.