Worldcat (a.k.a.OCLC). (Online)
Comprehensive database that serves as a major union catalog of records held in libraries around the world, including many major research and academic libraries; archives and museum libraries; law, medical, and theological libraries; art and music libraries; area studies collections; public and corporate libraries; historical societies and book clubs. Entries describe books, serials, archival collections, manuscripts, maps, music scores, sound recordings, films, photographs, posters, electronic resources, and more. The Catalog extends from the advent of printing to the present. New records are added daily.
Arcade / New York Art Resources Consortium. (Online)
Merged library catalogs of the Museum of Modern Art Library, the Frick Art Reference Library and the Brooklyn Museum of Art Libraries and Archives.
Deutsches Archäologisches Institut. Library. (Online)
Harvard University Libraries (a.k.a. Hollis). (Online)
Includes Fine Arts Library, Graduate School of Design, Villa I Tatti, Florence. Berenson Library, and more.
Metropolitan Museum of Art Library. (New York, N.Y.) (a.k.a. Watsonline). (Online)