The International Standard Book Number, or ISBN (sometimes pronounced "is-ben"), is a unique identifier for books, intended to be used commercially. 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. A similar identifier, the International Standard Serial Number (ISSN), is used for periodical publications such as magazines.
Each edition and variation (except reprints) of a book receives its own ISBN. The number is either 10 or 13 digits long, and consists of four or five parts:
- if 13-digit ISBN, an EAN prefix, either 978 or 979
- the country of origin or language code,
- the publisher,
- the item number, and
- a checksum character.
The different parts can have different lengths and are usually separated by hyphens. Hyphens are not strictly necessary however, since prefix codes are used which ensure that no two codes start the same way. If present, hyphens 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 isbn.org.
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. There is, in general, no requirement for a publisher to assign an ISBN to a book nor for that book to display its number - but see below for the exception in China. However, many bookstores will only deal with items bearing an ISBN.
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 may correspond to the same publisher.
The International ISBN Agency  in its official manual  states that the 10-digit ISBN check digit, which is the last digit of the 10 digit ISBN, is calculated on a modulus 11 with weights 10 to 2, using X in lieu of 10 where ten would occur as a check digit. This means that each of the first nine digits of the 10-digit ISBN – excluding the check digit itself – is multiplied by a number in a sequence from 10 to 2 and that the resulting sum of the products, plus the check digit, must be divisible by 11 without a remainder.
By this method the calculation for the 10-digit ISBN whose first nine digits are 0-306-40615 would be done thus:
10×0 + 9×3 + 8×0 + 7×6 + 6×4 + 5×0 + 4×6 + 3×1 + 2×5 = 0 + 27 + 0 + 42 + 24 + 0 + 24 + 3 + 10 = 130 The next complete multiple of 11 is 12×11 = 132 132 - 130 = 2
So the check digit is 2, and the complete sequence is ISBN 0-306-40615-2.
A second method to find the check digit is by first multiplying each digit of the 10-digit ISBN by that digit's place in the number sequence from 1 to 9, 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 10-digit 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 or two transposed digits) can always be detected.
EAN format used in barcodes, and planned upgrade
Currently, the barcodes found on the backs of books (or inside front covers of mass-market paperbacks) are EAN13; they may be "Bookland"—that is, with a separate barcode encoding five digits for the currency and recommended retail price. There is a detailed description of the EAN13 format here. "968", 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).
Because of a pending shortage in certain ISBN categories, the International Organization for Standardization (ISO) will migrate to a thirteen-digit ISBN in a process starting on 1 January 2005 and finishing 1 January 2007. This move will also bring the ISBN system into line with the UPC barcode system. There is a FAQ document about this change. Existing ISBNs will be prefixed with "978" (and the check digit recalculated); as the "978" ISBNs are exhausted, the "979" prefix will be introduced. This is expected to happen more rapidly outside of the US. Note that publisher identification codes are unlikely to be the same in 978 and 979 ISBNs.
Since the new 13-digit ISBNs will be identical to the EAN barcoded format of any existing 10-digit ISBNs, this process will not break compatibility with any existing barcodes. This means that moving to an EAN-based system will allow booksellers to use a single numbering system for both book and non-book products without breaking backwards compatibility with existing ISBN-based information, and with only minimal changes to their IT systems. For this reason, many booksellers, including Barnes & Noble, have already opted to start the process of phasing out usage of ISBNs in favour of using EAN codes as of March 2005.
ISBNs and book censorship in the People's Republic of China
ISBNs are used as a means of book censorship in the People's Republic of China. For a printer to legally print a run of books, they must have an ISBN, which are assigned in blocks to state owned publishing houses. However, since the 1990s, this means of censorship has become much less effective as state publishing houses, which, like all state owned enterprises, have been weaned from government subsidy, will now sell ISBNs to the highest bidder without regard to the content.
- ASIN (Amazon Standard Identification Number)
- ISMN (International Standard Music Number)
- ISAN (International Standard Audiovisual Number)
- ISSN (International Standard Serial Number)
- Library of Congress Control Number
- ISO 2108:2005 at www.iso.org
- Brief Summary of ISBN
- How to find a book from Wikibooks
- ISBN to EAN transition at isbn.org
- Description of the ISBN to EAN upgrade process at bookweb.org
- Wikipedia:ISBN, use of ISBN on Wikipedia
- National and international agencies
- International ISBN Agency - coordinates and supervises the world-wide use of the ISBN system.
- ISBN Agency Australia - Thorpe-Bowker, a division of R R Bowker LLC
- ISBN agency for UK and Republic of Ireland - Nielsen BookData
- ISBN agency for US and Puerto Rico - R.R. Bowker LLC
- Numerical List of Group Identifiers List of language/region prefixes
- 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.
- ISBNdb.com - find books by ISBN, author, title, subject, etc; auto-corrects ISBN checksums if needed.
- ISBN.nu - offers free searching of a titles database.
- Yet another ISBN lookup tool that searches a number of database and bookseller sites.
- RFC 3187 Using International Standard Book Numbers as Uniform resource names (URN)
- Online tool to produce barcodes from ISBNs.
- ISBN-13 For Dummies
- Implementation guidelines (pdf document) for the 13 digit ISBN code.
- The ISBN tools website has open-source java classes to implement 10 and 13-digit ISBNs.
^ Occasionally publishers will use an ISBN in error for more than one title (for example, the first edition of "The Ultimate Alphabet" and "The Ultimate Alphabet Answerbook" have the same ISBN). Conversely, 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.
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