Jacques de Vitry (†1240), a noted preacher in Brabant and Languedoc, served as canon regular of Saint-Nicholas d’Oignies (1211-16), bishop of Acre (1216-29) and auxiliary bishop of Liège (1226-29), and ultimately as cardinal-bishop of Tusculum (1229-1240). Whilst his letters, sermons, and the Historia Occidentalis have been extensively studied, the Historia Orientalis, Jacques’s encyclopedic work on the Holy Land, has so far escaped any such interest. Considered as yet another crusading history or pilgrimage guide drawing on previous writings, the few editions and brief studies of this work published since the nineteenth century are based neither on a detailed textual analysis nor on a complete investigation of the manuscript tradition. This thesis, therefore, addresses an important gap in the historiographical debate by providing a detailed analysis of the contents of the Historia Orientalis and its sources, in combination with an examination of the manuscript tradition up to the early fourteenth century. In it, I argue that the work is composed of different genres, each addressing a topic that served Jacques’s agenda and his activities as theologian, preacher, historian, pilgrim, and crusader. Moreover, by examining the rich manuscript tradition, I establish the book’s legacy and show that Jacques’s contemporaries perceived the text as an eclectic work. Jacques’s combination of different popular genres contributed to the influence of the text which is preserved in no fewer than 126 extant manuscripts. The thesis falls into three sections. In the first, I introduce my investigation and provide a long overdue revised biographical note and contextualisation of Jacques’s writings. In the four chapters of the second section, I analyse the text to see how Jacques combined the editing of existing source material with his personal knowledge into a work that served the reform and crusade agenda of the Fourth Lateran Council of 1215. The four chapters discuss the medieval genres that can be found in Jacques’s work: a history of the crusades, an account on Islam, a description of the Holy Land, and an ethnographical treatise. In the third section, using codicological research to discuss the text’s compilation, influence, readership, and legacy in the thirteenth and early fourteenth centuries, I argue that each genre found within the Historia was intended for and read by a different audience, thus explaining the wide appeal of the work as a whole. The sixth chapter focuses on the early manuscript tradition and dissemination of the Historia Orientalis while the seventh chapter addresses, on the one hand, the use of these manuscripts and the relationship to other texts in the same codex and, on the other hand, the authors who copied or used Jacques’s text in their own works. By combining a detailed textual analysis with extensive manuscript research, this investigation into the contents, readership and legacy of the Historia Orientalis sheds new light on the mechanisms behind the dissemination and influence of religious propaganda, as well as highlights Jacques’s seminal contribution to Church reform and the approach to crusading in the thirteenth century in accordance with the agenda set by the Fourth Lateran Council.