This is a study of relations between the Vatican and the Fascist regime in Italy in the most troubled and crucial phase of their relationship, the period 1929–32. It is the first time that any historian, either in Italy or elsewhere, has carried out a detailed and comprehensive study of the conflicts between the Vatican and Italian Fascism in these years; nor has there been any detailed analysis of the causes and the consequences of the crisis of 1931. As well as considering the various causes of conflict in this period, the author sets out what he believes to be the long-term consequences of the 1931 crisis, and in so doing challenges a number of previously accepted interpretations.