This dissertation investigates the use of ornament and calligraphy in the medieval manuscript known as the Book of Kells, as well as related manuscripts and other works of art. A copy of the four gospels of the Christian New Testament in Latin, the Book of Kells was made around 825, most likely at the monastery on the island of Iona, off the west coast of Scotland. The manuscript has long been famous for the density and complexity of its illumination, and its full-page miniatures and decorated initials have been the subject of numerous studies. My dissertation adds to our understanding of the book by looking at two sections that have not been the focus of previous study: a passage of four pages at the beginning of Matthew, folios 29v-31r, that feature seemingly unfinished borders and the full-page incipit to the Gospel of Luke on folio 188r. I demonstrate that the designers of the manuscript intentionally left the pages in Matthew unfinished as a way of expressing ideas about the nature of Christ and the relationship of the Old Testament to the New. The pages thus call attention to symbolic use of ornament in Insular art, and I subsequently show that several contemporary works use ornamental forms as a metaphor for the incarnate flesh of Christ. In my analysis of the Luke incipit page, I investigate the manipulation of letterforms in the Book of Kells and related works of art and describe the ways in which Insular scribes and painters imbued the abstract shapes of letters with meaning beyond their essential linguistic reference. As a whole, the dissertation demonstrates that ornament and calligraphy, rather than existing simply to beautify works of art, can be important bearers of meaning in of themselves.