The question of the biblical canon has never been a merely academic curiosity for the Catholic tradition. It touches the very heart of how the Church understands revelation, authority, and the transmission of divine truth across the centuries. To speak of "canon" is to speak of the living memory of God's people, the written testimony of salvation history, and the discernment of the Church guided by the Holy Spirit. The canon is not simply a list of books; it is the crystallization of the Church's faith, the textual expression of the apostolic proclamation, and the fruit of a long and complex historical journey. This book seeks to explore that journey from its earliest roots to the close of the fifth century, a period in which the foundations of the Christian biblical canon were laid with remarkable depth, diversity, and theological richness.