Beatus of Liébana was a monk, theologian, and author of the Commentary on the Apocalypse, an influential compendium of previous authorities' views on the Apocalypse. For him, the observation and reading of such works was a sacred action, akin to communion. Beatus treats the reading of the book as the same as the body, and so by reading the book, the reader is one with Christ. He also led the opposition against a Spanish variant of Adoptionism, the heretical belief that Christ was the son of God by adoption, an idea first propounded in Spain by Elipandus, the bishop of Toledo.

Commentary on the Apocalypse is a book written in the eighth century by the Spanish monk and theologian Beatus of Liébana (730–785) and copied and illustrated in manuscript in works called "Beati" during the 10th and 11th centuries AD. It is a commentary on the New Testament Apocalypse of John or Book of Revelation. It also refers to any manuscript copy of this work, especially any of the 27 illuminated copies that have survived. It is often referred to simply as the Beatus. The historical significance of the Commentary is made even more pronounced since it included a world map, which offers a rare insight into the geographical understanding of the post-Roman world. Well-known copies include the Morgan, the Saint-Sever, the Gerona, the Osma and the Madrid Beatus codices.