For information on using ISBNs in wikipedia: see wikipedia:ISBN
The International Standard Book Number (ISBN) is a unique identifier for a book. The ISBN system was created in the United Kingdom in 1966 (then called Standard Book Numbering SBN) and adopted as international standard ISO 2108 in 1970.
Each edition and variation (except reprints) of a book receives its own ISBN. The number consists of four parts:
The country field is 0 or 1 for English speaking countries, 2 for French speaking countries, 3 for German speaking countries etc. The country field can be up to 5 digits long; 99936 for instance is used for Bhutan. See this complete list.
The publisher number is assigned by the national ISBN agency, and the item number is chosen by the publisher.
Publishers receive blocks of ISBNs, with larger blocks going to publishers that are expected to need them; a small publisher might receive ISBNs consisting of a digit for the language, seven digits for the publisher, and a single digit for the individual items. Once that block is used up, the publisher can receive another block of numbers, with a different publisher number. As a consequence, different publisher numbers occasionally correspond to the same publisher.
The check digit is the sum of the digit number times the digit, modulo 11, with "10" represented by the character "X". For example, to find the check digit for the ISBN whose first nine digits are 0-306-40615:
1·0 + 2·3 + 3·0 + 4·6 + 5·4 + 6·0 + 7·6 + 8·1 + 9·5 = 0 + 6 + 0 + 24 + 20 + 0 + 42 + 8 + 45 = 145 = 13·11 + 2So the check digit is 2, and the complete sequence is ISBN 0-306-40615-2. Since 11 is a prime number, this scheme ensures that a single error (in the form of an altered digit) can always be detected.
Because of a pending shortage in certain ISBN categories the international standards organization will soon be moving to a thirteen digit ISBN. This move will also bring the ISBN system into line with the UPC barcode system. There is a FAQ document about this change.