The Online Encyclopedia and Dictionary







The International Standard Book Number, or ISBN (sometimes pronounced "is-ben"), is a unique identifier for books, intended to be used commercially. There is another quite similar system, the International Standard Serial Number (ISSN), for periodical publications such as magazines. The ISBN system was created in the United Kingdom in 1966 by the booksellers and stationers W H Smith and originally called Standard Book Numbering or SBN. It was adopted as international standard ISO 2108 in 1970.



Each edition and variation (except reprints) of a book receives its own ISBN. The number is always 10 digits long, and consists of four parts:

  1. the country of origin or language code,
  2. the publisher,
  3. the item number, and
  4. a checksum character.

The different parts can have different lengths and are usually separated by hyphens. These hyphens are not strictly necessary however, since prefix codes are used which ensure that no two codes start the same way. If present, they must be placed correctly (instructions are given here); however they are not sufficient since different agencies are responsible for allocating different ISBN subranges and a complete, up-to-date list is not available at

The country field is 0 or 1 for English speaking countries, 2 for French speaking countries, 3 for German speaking countries, etc. (The original SBN lacked the country field, but prefixing 0 to a 9-digit SBN creates a valid ISBN.) 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 of an ISBN can be found by first multiplying each digit of the ISBN by that digit's place in the number sequence, with the leftmost digit being multiplied by 1, the next digit by 2, and so on. Next, take the sum of these multiplications and calculate the sum 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 + 2

So 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.

Planned upgrade

Because of a pending shortage in certain ISBN categories the International Organization for Standardization will be moving to a thirteen digit ISBN starting on 1 January 2007. This move will also bring the ISBN system into line with the UPC barcode system. There is an FAQ document about this change. Existing ISBNs will be prefixed with "978" (and the check digit recalculated); when the "978" ISBNs are exhausted, the "979" prefix will be introduced. Note that publisher identification codes are unlikely to be the same in 978 and 979 ISBNs. Many booksellers, including Barnes & Noble, have instead opted to begin a process of phasing out usage of ISBNs as of March 2005. They have instead adopted the more universal standard of EAN, since this applies to all media and not just books. It is unclear how this affects the planned ISBN upgrade.

EAN format used in barcodes

Currently, the barcodes found on the backs of books (or inside front covers of mass-market paperbacks) are EAN13; they may be "Bookland" - i.e. with a separate barcode encoding five digits for the currency and recommended retail price. There is a detailed description of the EAN13 format here. "978", the asset code for books, is prepended to the ISBN in the barcode data, and the check digit is recalculated according to the EAN13 formula (modulo 10, 1x and 3x weighting on alternate digits).

See also

  • ASIN (Amazon Standard Identification Number)
  • ISMN (International Standard Music Number)
  • ISAN (International Standard Audiovisual Number)
  • ISSN (International Standard Serial Number)
  • LCCN (Library of Congress Control Number)


Uniqueness was not always maintained, for example the first edition of "The Ultimate Alphabet" and "The Ultimate Alphabet Answerbook" have the same ISBN, and at least one book has been published with four ISBN numbers printed inside, depending on the binding and which of the two joint publishers were deemed applicable to a particular copy.

External links

National and international agencies
Online tools
  • Kimba Kano - Internet Explorer and Firefox add-on adding built in ISBN & ASIN searching.
  • ISBN check form checks checksum; outputs list of possible correct ISBN when the input is incorrect.
  • - find books by ISBN, author, title, subject, etc; auto-corrects ISBN checksums if needed.
  • - offers free searching of a titles database.
  • RFC 3187 Using International Standard Book Numbers as Uniform resource names (URN)
  • Online tool to produce barcodes from ISBNs.
  • Implementation guidelines (pdf document) for the 13 digit ISBN code.

Last updated: 05-13-2005 07:56:04