The article summarizes the state of knowledge about the role of religions during the First World War in Italy, with particular reference to their presence in society, in the trenches, in politics. Although also taking into account minority denominations, it devotes specific attention to Catholicism and the attitude to the war of the Catholic Church and the Holy See: a choice dictated not only by the fact that Catholicism was deeply rooted in the country, but also by the current lack of studies on the other faiths.