Research Guides: Resources for Rare Books: An Annotated Bibliography: General Reference Resources

Online Databases

Rarebooks.info Bibliography of works on rare books available for consultation. Comprises over 600,000 pages of key out-of-print bibliographies that can be browsed online.
Hathi Trust, Google Books, Internet Archive Text Archive Digital repositories that often contain digital copies of classic reference works and auction catalogues.

Glossaries, Encyclopedias, and Dictionaries

Carter, John. ABC for Book Collectors. Rev. by Nicholas Baker. New Castle, DE: Oak Knoll Press; London: British Library, 2006. Available online via ILAB. The standard resources for definitions of common bibliographical terms used in the field of rare books.
Glaister, Geoffrey Ashall. Encyclopedia of the Book. Second edition. New introduction by Donald Farren. New Castle, Delaware: Oak Knoll Books, 1996. Reprint of Glaister's Glossary of the Book: Terms Used in Papermaking, Printing, Bookbinding and Publishing with Notes on Illuminated Manuscripts and Private Presses.