After a historical excursus on the slow emergence of local clergy in various mission territories, as well as the international setting of Maximum Illud, the author makes a presentation of the apostolic letter of Pope Benedict XV and its content. As far as Catholic missions were concerned, the author sees the publication of Maximum Illud as one of the epoch-making events of the twentieth century. The reason is that Pope Benedict XV in his apostolic letter of November 30, 1919 considered the missions of the Catholic Church from a perspective that was truly universal, geared towards assuring them a firm rooting through the emergence of native or local churches outside the shores of Europe. In the final analysis, his research highlights the leadership role of Benedict XV in shaping Catholic missionary policies for the greater part of the twentieth century.