The International Standard Book Number (ISBN) is a unique, numerical commercial book identifier, based upon the 9-digit Standard Book Numbering (SBN) code created in the UK by the booksellers and stationers W.H. Smith and others in 1966. The 10-digit International Standard Book Number (ISBN) format was developed by the International Organization for Standardization and published as an international standard, ISO 2108, in 1970. (However, the 9-digit SBN code was used in the UK until 1974.) Currently, the ISO TC 46/SC 9 is responsible for the standard.

Since 1 January 2007, International Standard Book Numbers have been of 13 digits, compatible with Bookland EAN-13s.

A similar numeric identifier, the International Standard Serial Number (ISSN) identifies periodical publications such as magazines.

Overview

An ISBN is assigned to each edition and variation (except reprintings) of a book. The ISBN is 13 digits long if assigned after January 1, 2007, and 10 digits long if assigned before 2007. An International Standard Book Number consists of 4 or 5 parts:

1. for a 13 digit ISBN, a GS1 prefix: 978 or 979
2. the group identifier, (language-sharing country group)
3. the publisher code,
4. the item number, and
5. a checksum character or check digit.

The ISBN parts may be of different lengths, and usually are separated with hyphens or spaces.

The group identifier is a 1 to 5 digit number. The single digit group identifiers are: 0 or 1 for English-speaking countries; 2 for French-speaking countries; 3 for German-speaking countries; 4 for Japanese; 5 for Russian, and 7 for Chinese. An example 5 digit group identifier is 99936, for Bhutan. The original standard book number (SBN) had no group identifier, but affixing a zero (0) as prefix to a 9-digit SBN creates a valid 10-digit ISBN. Group identifiers form a prefix code; compare with country calling codes.

The national ISBN agency assigns the publisher number (cf. the :category:ISBN agencies); the publisher selects the item number. Generally, a book publisher is not required to assign an ISBN, nor for a book to display its number (except in China; see below), however, most book stores only handle ISBN-bearing merchandise.

A listing of all the 628,000 assigned publisher codes is published, and can be ordered in book form (€558, US$915.46). The web site of the international ISBN agency does not offer any free method of looking up publisher codes.

Publishers receive blocks of ISBNs, with larger blocks allotted to publishers expecting to need them; a small publisher may receive ISBNs of one or more digits for the group identifier code, several digits for the publisher, and a single digit for the individual items. Once that block of ISBNs is used, the publisher may receive another block of ISBNs, with a different publisher number. Consequently, a publisher may have different allotted publisher numbers. There also may be more than one group identifier used in a country. This might occur if a popular identifier has used up all of its numbers. The cited list of identifiers shows this has happened in China and in more than a dozen other countries.