Résumé : This thesis aims to present the ins and outs of the promotion of peace in the pontifical discourse from 1978 to 2021, based mainly on the speeches delivered by Popes John Paul II, Benedict XVI and Francis on the occasion of the World Day of Peace, the 1st of January of each year.Peace is a central theme in Catholic doctrine: already present in the Bible and in Christian tradition, it is progressively integrated into the official texts of the Roman Catholic Church, gradually forming the basis of the Holy See’s discourse. With the encyclical Pacem in Terris (1963), Pope John XXIII made the promotion of peace a papal priority. In 1992, the publication of the Catechism of the Catholic Church extended this prerogative to the entire community, and particularly to heads of State.The annual addresses of Peter’s successors have identified several threats to peace, first and foremost war, but also totalitarianism, social and economic injustices, and lack of fraternity and care for nature. According to them, peace is not only the absence of war, but a state where the essential principles of human life are respected, both for individuals and for nations.The popes also highlighted the various factors that can contribute to the strengthening of peace: the three main ones, according to them, are the protection of human dignity and human rights, including religious freedom and the right to life; respect for the international order, strengthened by dialogue and law; and finally, integral human development, which is based, among other things, on culture, the family and education. In short, peace must be founded on pillars capable of sustaining this edifice in the long term: every human being of good will is therefore invited to contribute to it.The last three pontiffs, both in their singularity and in respect for papal continuity, have all produced a singular and unique irenic discourse on the international scene to promote peace. This discourse’s study is part of the “Peace Studies” school that states that international relations should also be studied and understood through the prism of peace, and not only the ones of power or war.