The monumental work of renowned twentieth-century Swiss ecclesiologist Charles Journet, The Church of the Word Incarnate is among the most comprehensive and spiritually profound studies of the mystery of the Church. Presented here for the first time in English translation is Journet’s complete five-volume “essay in speculative theology,” in which he undertakes a Thomistic presentation of the Church in light of her four causes—efficient, material, formal, and final—corresponding to her four marks of apostolicity, catholicity, unity, and sanctity. In this first volume, Journet examines the apostolic hierarchy—the Twelve chosen by Christ, along with their successors and collaborators—as the Church’s immediate and instrumental efficient cause. After an initial consideration of the prior stages involved in the divine institution of the Church, Journet devotes much of the rest of the volume to the apostolic hierarchy itself and to its unified exercise of its distinct sacramental and jurisdictional powers, from which the Church’s existence in the world flows. The volume concludes with his reflections on apostolicity as both a property and sign of the true Church.