The International Standard Book Number (ISBN) is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster.
The 10-digit ISBN format was developed by the International Organization for Standardization (ISO) and was published in 1970 as international standard ISO 2108. However, the 9-digit SBN code was still used by United Kingdom publishers until 1974. An SBN is converted to an ISBN by appending a zero on the left.
After January 1, 2007, ISBNs changed to contain 13 digits, a format that is compatible with the European Article Number (EAN-13), as well as agreeing with the older 13 digit code known as Bookland.
The new ISBN separates its parts (prefix, language group, publisher, title number and check digit) with either a hyphen or a space. Other than the check digit and prefix, no part of the ISBN will have a fixed number of digits. "The elements must be separated clearly by hyphens or spaces when displayed in human readable form. Of the five elements, the middle three will be of variable lengths; the EAN prefixes as currently defined (i.e., '978' or '979') and the check digit lengths will remain fixed".
Each publisher is given a specific publisher number, as well as a block of numbers to use for their books. Each title or revised edition must have its own ISBN number.
- Solomon, David (2005). Coding for Data and Computer Communications. New York: Springer. p. 37-38. ISBN 0-387-21245-6.
- TC 46/SC 9. "Frequently Asked Questions about the new ISBN standard from ISO". LAC-BAC. http://www.lac-bac.gc.ca/iso/tc46sc9/isbn.htm. .
-  Book Industry Study Group FAQ