International ISBN Agency - Includes a user's manual, prefix ranges, details of group agencies, publications, reports, and news.
ISBN Tools - Information and tools for using International Standard Book Numbers. Scan them with a CueCat, look them up, or search them.
ISBN.org - Enables applications to be made for ISBNs, SANs, and ISMNs in the United States and Puerto Rico, and provides information about the standards.