This work argues that many early Christian quotations of the Old Testament derive not from scriptural manuscripts, but rather from authoritative written testimonia collections developed to support basic Christian beliefs. Combining recent patristic studies (notably on Justin and Barnabas) and evidence from Qumran with detailed examination of quotations in the New Testament, the book builds a fresh case for a neglected scholarly hypothesis. After reviewing the scholarly literature and analogous Jewish and Greco-Roman literary collections, the book presents a comprehensive overview of extant testimonia traditions from the second to the fourth century C.E. The final chapters argue for the use of written testimonia collections in the New Testament. This study offers solid evidence for a remarkably unified early Christian scriptural tradition that extended throughout the Mediterranean world.