ZVAB
- Search for old, rare and out-of-print books. Access to many bookstores. Bilingual, English and German.
- http://www.zvab.com/

Biblion Ltd.
- Antiquarian and rare books from primarily UK book dealers available on a searchable database.
- http://biblion.co.uk/

Library Book Sales
- Matching book buyers with quality books that have been donated to libraries or are duplicate copies, monographs or surplus materials. Ex-libris titles are discouraged but not excluded. Library types participating: public, private, institutional, specia
- http://www.librarybooksales.org/

Biblio.com, Inc.
- Searches databases of associated independent booksellers worldwide.
- http://www.biblio.com/

Ardis Online Database
- Searchable database of secondhand books from UK booksellers.
- http://www.ardis.co.uk/index.html

Used Books Search
- Search for used, rare and out of print books.
- http://www.usedbooksearch.co.uk

Antiquarian Books in Scandinavia
- Search the databases of the Scandinavian members of ILAB, International League of Antiquarian Booksellers.
- http://www.antikvariat.net/

Cover to Cover Antiquarian Books
- Offering a range of antiquarian, second hand and out of print books.
- http://www.covers.freeuk.com/

Big Words
- Compares textbook prices at four stores - buying or selling.
- http://www.bigwords.com

ABooksearch.com
- Searches databases of participating booksellers.
- http://www.abooksearch.com/

BookSearcher.org
- Large online database of used, rare, hard to find, out of print, antiquarian and collectible books.
- http://www.booksearcher.org/

Abebooks.com
- Offering new, used, rare and out of print books, textbooks, and ephemera. Represents a wide variety of independent booksellers located throughout the world.
- http://www.abebooks.com/

Bibliopoly
- Multilingual, international search for antiquarian and rare books.
- http://www.bibliopoly.com/

TomFolio.com
- Searchable database of used, rare and collectible books from a group of booksellers.
- http://www.tomfolio.com/

Bibliophile
- Multilingual book search engine.
- http://www.bibliophile.net/

Used Book Central
- Searches the stock of affiliated dealers in the US.
- http://www.usedbookcentral.com/