Book excerpt: In this volume the McGill University Research Group on Transmission, Translation, and Transformation in Medieval Cultures and their collaborators initiate a new reflection on the dynamics involved in receiving texts and ideas from antiquity or from other contemporary cultures. For all their historic specificity, the western European, Arab/Islamic and Jewish civilizations of the Middle Ages were nonetheless co-participants in a complex web of cultural transmission that operated via translation and inevitably involved the transformation of what had been received. This three-fold process is what defines medieval intellectual history. Every act of transmission presumes the existence of some 'efficient cause' - a translation, a commentary, a book, a library, etc. Such vehicles of transmission, however, are not passive containers in which cultural products are transported. On the contrary: the vehicles themselves select, shape, and transform the material transmitted, making ancient or alien cultural products usable and attractive in another milieu. The case studies contained in this volume attempt to bring these larger processes into the foreground.They lay the groundwork for a new intellectual history of medieval civilizations in all their variety, based on the core premise that these shared not only a cultural heritage from antiquity but, more importantly, a broadly comparable 'operating system' for engaging with that heritage.Each was a culture of transmission, claiming ownership over the prestigious knowledge inherited from the past. Each depended on translation. Finally, each transformed what it appropriated.