In 1980, the Catholic Church in the Democratic Republic of the Congo (called Zaire at the time) celebrated the centenary of the evangelization of the country. Thanksgiving to God was associated with a lively recognition of the patient and wise apostolic work of the many missionaries, bishops, priests, men and women religious of the past and present. To some was recognized the love of the Congo to the point of devoting their lives to initiate the local populations to the Gospel, to consider them capable of forming a local Church and to prepare their Pastors. To others, Pope John Paul II expressed, in Kinshasa, on May 3, 1980, his gratitude for the good work accomplished by the local clergy and the lay catechists to nourish the faith of the faithful and maintain the vitality of the Church throughout the country.We can see it well. The dimension of the relations of the Catholic Church with the State is absent. In this thesis we try to reconstruct, through the analysis of both diplomatic-legal and historical-political facts, the undisputed existence of bilateral relations between the Church and the Congo from the foundation of the latter. For us, the evangelization that counts until today (that is, the phase that began in 1880) is the fruit of the combined efforts of Church and State. This is for two obvious reasons. Firstly, Leo XIII, who is the pope contemporary with the creation of the State in the Congo, had engaged the relations of the Catholic Church with the States in a perspective of wise union and perfect harmony. The Roman centralization of missionary activity, while curbing the misdeeds of the right of patronage, opened the Church to agreements and bilateral agreements with the States of/in the mission countries. Secondly, in the case of the Congo, the State of the Congo, first in gestation and then fully constituted, had always displayed its desire to ally itself with the Church in the hope that their respective missions (civilizing and evangelizing) bear the expected fruits.Admittedly, the relations of ...