| By Popularity
| Alphabetical (What's This?)|
- Oak Knoll Books
Specializes in out-of-print books about book collecting, book history and the book arts; publisher, distributor, and bookseller.
- Octavo Corporation
Publishes digital editions of rare books and manuscripts.
- Odd Volumes United
Bringing together sellers and buyers of missing volumes, dust jackets, and periodicals.
- Odyssey Books
Deal in used and rare books of literary quality, specializing in fiction but also including 30 other categories.
- Old Book Shop, The
Specializes in used, out of print, and rare hardback books.
Features an extensive inventory of vintage, used, and rare cookbooks.
- Olympia Books
Specializes in unusual, rare, and out of print books for scholars and collectors.