Medieval books that survive today have been through a lot: singed by fire, mottled by mold, eaten by insects, annotated by readers, cut into fragments, or damaged through well-intentioned preservation efforts. In this book, Michelle Warren tells the story of one such manuscript—an Arthurian romance with textual origins in twelfth-century England now diffused across the twenty-first century internet. This trajectory has been propelled by a succession of technologies—from paper manufacture to printing to computers. Together, they have made literary history itself a cultural technology indebted to colonial capitalism. Bringing to bear media theory, medieval literary studies, and book history, Warren shows how digital infrastructures change texts and books, even very old ones. In the process, she uncovers a practice of "tech medievalism" that weaves through the history of computing since the mid-twentieth century; metaphors indebted to King Arthur and the Holy Grail are integral to some of the technologies that now sustain medieval books on the internet. This infrastructural approach to book history illuminates how the meaning of literature is made by many people besides canonical authors: translators, scribes, patrons, readers, collectors, librarians, cataloguers, editors, photographers, software programmers, and many more. Situated at the intersections of the digital humanities, library sciences, literary history, and book history, Holy Digital Grail offers new ways to conceptualize authorship, canon formation, and the definition of a "book."