It has long been argued that Tatian, in the production of the Diatessaron, made regular reference to the Old Testament Peshitta when he came across Old Testament citations in the Gospels. This book argues on the contrary that Tatian made little or no use of the Old Testament Peshitta, but regularly took over the text of the Old Testament citations as he found them in the Gospel sources out of which he created his harmony. Where they differ from the form of these citations in the standard Greek text tradition of the Gospels, it is because, in the second century, Tatian had access to Gospel sources which may have varied significantly from the text of the later manuscripts on which our modern critical editions are based. Thus, Tatian's Diatessaron becomes a window into an early state of the Gospel texts and supports the idea that a significant amount of textual fluidity characterized the Gospel texts in the first two centuries of their transmission. This study will be of interest to those working in the fields of Diatessaronic studies, New Testament Textual Criticism, and the history of the Syriac Church.