Despite its enormous popularity and wide circulation in the early church, rarely do NT introductions mention Tatian’s (T) Diatessaron (D). If mentioned at all, the thin summary provided readers features D as the antagonist (among others) in the complicated history of the earliest reception of the canonical Gospels prior to Irenaeus’s witness of their fourfold collection in Against Heresies. Not only is mention often made of T’s alleged heterodoxy but that his “Gospel of the Connected,” as Ephraen the Syrian called it, presents the earliest example of Gospel harmonization found wanting by modern criticism, which smooths over the awkward diversity of the four Gospels. Moreover, the sheer scope of Diatessaronic studies—the languages one needs to master, the manuscript traditions one needs to control, the awareness of the sociohistorical diversity that marks out D’s trajectory into the ecclesial east and west—easily frustrates the faint of scholarly heart.This third offering in T&T Clark’s Reception of Jesus in the First Three Centuries series, then, may be read as a welcome response to this neglect. First presented as seminar papers at two successive SBL meetings (2016–17), this collection gathers the findings of several prominent voices in D research not only to rehabilitate the academy’s interest in T’s Gospel—its occasion, its genre, its production, and its reception history—but to recognize it as indispensable to better understand the earliest history of the church’s reception of its canonical Jesus.The moderator and coeditor of this collegium, Michael R. Crawford, directs the program in Early Christian Studies at the Australian Catholic University (Melbourne). He succeeds in his role the volume’s dedicatee, the late Tjitze Baarda, a colleague of immense learning whose final work is published in this volume. Nicholas J. Zola of Pepperdine University (USA) joins Crawford as coeditor of this impressive collection.The book’s evocative title, The Gospel of Tatian, cues the collection’s principal research question: how should we regard the genre and purpose of T’s D, whether as a Gospel of his own invention created to respond to issues of his second-century Syrian church or did he fashion D as a postbiblical “gospel harmony” that not only witnessed the canonical status of the four canonical Gospels but provided a supplement for their collected use as a fourfold but integral whole? In response, nine chapters are gathered in three discrete sections to fashion a logical sequence of three interpenetrating research interests.Part 1 consists of three essays that seek to trace the sources T used to fashion D. Appropriately, the late T. Baarda’s final study is placed first to raise the programmatic question about the nature and purpose of D’s origins. Baarda understands T’s religious origins—his conversion, his education, his world travels—as a source. He also notes the origins of written histories of Jesus from competing oral sources of a highly fluid (and contested) tradition. Critically, Baarda notes that T’s use of John’s Gospel to cue and complete D’s history of Jesus not only intended to smooth disagreements between rival Jesus traditions but to introduce a history of Jesus that could participate in the philosophical, more secular discussions of Christianity in his world. The next two essays by Charles E. Hill (Reformed Theological Seminary) and Jan Joosten (Oxford) take different sides on whether, as W. L. Peterson argued, T used extracanonical Gospels to fill out his history of Jesus. Hill concludes his exhaustive study that the traces of extracanonical Gospels Peterson found in D were most likely added later to T’s original composition. The only written Gospels T used were the canonical four, which he treated as authoritative. While Hill does not answer the question whether T intended D as a replacement Gospel, the subtext of his incisive study implies not. Allowing for the absence of a “base-text” as well as the complex history of D’s reception in the east and west, Joosten takes a case study and more subtle approach to the question of sources: he traces T’s redaction of the fourfold Gospel’s mention of “Jewish law” to the influence of extracanonical Gospel traditions in the east (e.g., Ephraem’s Syriac commentary) but then backward from D to a pre-canonical Gospel tradition in the Latin west. His study affirms Peterson’s claims of T’s use of extracanonical sources.Part 2 goes to the heart of this collection by considering D’s genre and so also its intended purpose. Francis Watson (Durham) argues against the common view that D is a “Gospel harmony” thereby supplementing the use of the canonical four. He shows that T followed the pattern of other Evangelists, especially set out in Luke’s prologue (which also opens D), to draw on and edit the best available sources to compose a more complete history of Jesus’s life. That is, Watson considers the production of D as the decisive element in settling the question of its nature. Quite apart from the question of sources, Watson considers it plausible—given the sheer number of Gospels in circulation during the second century and the epistemic crisis produced by the evident differences between them—that T wrote his own Gospel as a canonical story of Jesus against which all other Gospels, preached or written, were measured. Nicholas Perrin (Wheaton) follows Watson’s masterful study with one of his own that applies genre criticism to the kind of Gospel T actually produced—that is, his beginning point is not the process of writing his Gospel (so Watson) but the form it actually took. By tracing the influence of Justin’s use of the canonical Gospels on T and also the reception of D as a template for future Gospel harmonies, Perrin is able to argue that an enduring function of D when read as a Gospel harmony was both apologetical (problem of competing Jesus traditions) and pedagogical (usefulness in teaching a single account of Jesus’s life). Actually, James W. Baker (Western Kentucky) elaborates Perrin’s conclusion by showing that, from the moment oral traditions of Jesus were edited and written down as Gospels (AD 70–110), different Christian communities had access to multiple Gospels. In this sense, Gospel collection was a constitutive element of Gospel composition and repeated use in worship and catechesis. T would naturally have read and used the four canonical Gospels to produce his own Gospel without thought of replacing them with his own. It was the common practice of the literate elite of his world to collect, read, and use multiple histories of important figures. Even the singularity of T’s history of Jesus—a “Gospel of the connected”—is no different from the church’s perception that the four different canonical Gospels formed an integral whole—a “Gospel of the separated” that traveled together in codices titled by the singular “Gospel.”Part 3 concludes the collection by considering the various witnesses to D and its subsequent performances, whether they realize T’s original vision (however this is understood). Ian Mills (Duke) challenges the unguarded claims made by most of those scholars who contributed to this volume (!) that the Dura fragment is not from D nor is even Diatessaronic. The linguistic links that have secured this claim are insufficiently precise and, at best, the Dura finding—still important—is of another Gospel harmony entirely, perhaps one that trades on T’s invention. With the Dura hypothesis in shambles, Ulrich B. Schmid (Wuppertal) reconsiders Codex Fuldensis, especially its paratextual elements, whether we can still consider it a sixth-century Latin witness to D. In his highly technical and demanding study, Schmid agrees that Fuldensis stands as the single most important witness to D in the west, independent of “its Vulgate dress” comparable in its reception and redaction of D with that of Ephrem and the Arabic D of the east. The collection’s final essay by Nicholas Zola considers the ambivalence of D’s treatment in the textual criticism of the Gospels since Mill (1707). From observations based on his careful survey, Zola concludes that “direction is needed in the field of Diatessaronic studies” (p. 230). Presuming this, he concludes the volume with a discussion of seven research questions that envision a productive future not only of D but of its relationship to the study of the early reception of written Gospel traditions, the formation of a fourfold Gospel canon, and the text-critical apparatus of the Greek NT. Zola’s outline of “next steps” is as bracing as it is promising.This collection is appended by a comprehensive bibliography and an excellent subject index to facilitate its use in research. I highly recommend this collection for all who are interested in the reception and formation of the Gospel canon and its ongoing textual criticism. It stands as a much needed resource (and often corrective) in our understanding of the form and function of Titian’s Diatessaron.