You could pay $118 on Amazon for the Metropolitan Museum of Art’s catalog The Art of Illumination: The Limbourg Brothers and the Belles Heures of Jean de France, Duc de Berry. Or you could pay $0 to download it at MetPublications, the site offering “five decades of Met Museum publications on art history available to read, download, and/or search for free.” If that strikes you as an obvious choice, prepare to spend some serious time browsing MetPublications’ collection of free art books and catalogs.