In this two-volume work, J. Rendel Harris (1852-1941) fundamentally shaped Biblical scholarship in the twentieth century, arguing for the existence of a 'first known treatise on Christian theology', antedating the New Testament. A palaeographer, Harris examined recurring textual corruptions of Old Testament passages in early Christian writers and surmised an underlying collection, which he called the 'Testimony Book'. The book, Harris believed, collected Biblical testimonia - passages prophesying Christ - in order to prove the legitimacy of the new Christian faith. These arguments against Judaic theology marked, in Harris's opinion, the beginnings of the Christian written tradition. Volume 1 (1916) lays the groundwork for Harris's argument by examining the use of testimonia in early Christian writers like Cyprian and Gregory of Nyssa. 'The starting point of the modern study of the use of the Old Testament in the New', this is a work of enduring importance to religion scholars.