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.
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 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.
By using variable block lengths, a large publisher will have few digits allocated for the publisher number and many digits allocated for titles; likewise countries publishing much will have few allocated digits for the group identifier, and many for the publishers and titles. Here are some sample ISBN-10 codes, illustrating block length variations.
|ISBN||Country or area||Publisher|
|80-902734-1-6||Czech Republic; Slovakia||Taita Publishers|
|1-84356-028-3||United Kingdom||Simon Wallenberg Press|
|0-8044-2957-X||English-speaking area||Frederick Ungar|
|0-85131-041-9||English-speaking area||J. A. Allen & Co.|
|0-9752298-0-X||English-speaking area||KT Publishing|
For example, the check digit for an ISBN-10 of 0-306-40615-? is calculated as follows:
s = 0×10 + 3×9 + 0×8 + 6×7 + 4×6 + 0×5 + 6×4 + 1×3 + 5×2
= 0 + 27 + 0 + 42 + 24 + 0 + 24 + 3 + 10
130 / 11 = 11 remainder 9
11 - 9 = 2
Thus, the check digit is 2, and the complete sequence is ISBN 0-306-40615-2.
Formally, the check digit calculation is:
If the result is 11, a '0' should be substituted; if 10, an 'X' should be used.
The two most common errors in handling an ISBN (e.g., typing or writing it) are an altered digit or the transposition of adjacent digits. Since 11 is a prime number, the ISBN check digit method ensures that these two errors will always be detected. However, if the error occurs in the publishing house and goes undetected, the book will be issued with an invalid ISBN.
The ISBN-10 check-digit can also be calculated in a slightly easier way:
The calculation of an ISBN-13 check digit begins with the first 12 digits of the thirteen-digit ISBN (thus excluding the check digit itself). Each digit, from left to right, is alternately multiplied by 1 or 3, then those products are summed modulo 10 to give a value ranging from 0 to 9. Subtracted from 10, that leaves a result from 1 to 10. A zero (0) replaces a ten (10), so, in all cases, a single check digit results.
For example, the ISBN-13 check digit of 978-0-306-40615-? is calculated as follows:
s = 9×1 + 7×3 + 8×1 + 0×3 + 3×1 + 0×3 + 6×1 + 4×3 + 0×1 + 6×3 + 1×1 + 5×3
= 9 + 21 + 8 + 0 + 3 + 0 + 6 + 12 + 0 + 18 + 1 + 15
93 / 10 = 9 remainder 3
10 – 3
Thus, the check digit is 7, and the complete sequence is ISBN 978-0-306-40615-7.
Formally, the ISBN-13 check digit calculation is:
This check system — similar to the UPC check digit formula — does not catch all errors of adjacent digit transposition. Specifically, if the difference between two adjacent digits is 5, the check digit will not catch their transposition. For instance, the above example allows this situation with the 6 followed by a 1. The correct order contributes 3×6+1×1 = 19 to the sum; while, if the digits are transposed (1 followed by a 6), the contribution of those two digits will be 3×1+1×6 = 9. However, 19 and 9 are congruent modulo 10, and so produce the same, final result: both ISBNs will have a check digit of 7. The ISBN-10 formula uses the prime modulus 11 which avoids this blind spot, but requires more than the digits 0-9 to express the check digit.
Currently, the barcodes on a book's back cover (or inside a mass-market paperback book's front cover) are EAN-13; they may have a separate barcode encoding five digits for the currency and the recommended retail price. The number "978", the Bookland "country code", 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).
Partly because of a pending shortage in certain ISBN categories, the International Organization for Standardization (ISO) migrated to a thirteen-digit ISBN (ISBN-13); the process began January 1, 2005 and was to conclude January 1, 2007. Thirteen-digit ISBNs are prefixed with "978" (and the check digit recalculated); as the "978" ISBN supply is exhausted, the "979" prefix will be introduced. This is expected to occur more rapidly outside the United States; originally, "979" was the "Musicland" code for musical scores with an ISMN, however, ISMN codes will differ visually as they begin with an "M" letter; the bar code represents the "M" as a zero (0), and for checksum purposes it will count as a 3.
Publisher identification code numbers are unlikely to be the same in the "978" and "979" ISBNs, like-wise, there is no guarantee that language area code numbers will be the same. Moreover, the ten-digit ISBN check digit generally is not the same as the thirteen-digit ISBN check digit. Because the EAN/UCC-13 is part of the Global Trade Item Number (GTIN) system (that includes the EAN/UCC-14, the UPC-12, and the EAN-8), it is expected that ISBN-generating software should accommodate fourteen-digit ISBNs.
Barcode format compatibility is maintained, because (aside from the group breaks) the ISBN-13 barcode format is identical to the EAN barcode format of existing ISBN-10s. So, migration to an EAN-based system allows booksellers the use of a single numbering system for both books and non-book products that is compatible with existing ISBN-based data, with only minimal changes to information technology systems. Hence, many booksellers (e.g. Barnes & Noble) migrated to EAN barcodes as early as March 2005. Although many American and Canadian booksellers have been able to read EAN-13 barcodes before 2005, most general retailers could not read them. The upgrading of the UPC barcode system to full EAN-13, in 2005, eased migration to the ISBN-13 in North America. Moreover, by January 2007, most large book publishers added ISBN-13 barcodes alongside the ten-digit ISBN barcodes of books published before January 2007.
Publishers and libraries have varied policies about the use of the ISBN check digit. Publishers sometimes fail to check the correspondence of a book title and its ISBN before publishing it; that failure causes book identification problems for libraries, booksellers, and readers.
Most libraries and booksellers display the book record for an invalid ISBN issued by the publisher. The Library of Congress catalogue contains books published with invalid ISBNs, which it usually tags with the phrase "Cancelled ISBN". However, book-ordering systems such as Amazon.com will not search for a book if an invalid ISBN is entered to its search engine.