View source for International Standard Book Number

{{Selfref|For the usage of ISBNs in Wikipedia, see [[Wikipedia:ISBN]]}}
[[File:EAN-13-ISBN-13.svg|thumb|300px|A 13-digit ISBN, 978-3-16-148410-0, as  represented by an [[International Article Number (EAN)|EAN-13 bar code]].]]
The '''International Standard Book Number''' ('''ISBN''') is a unique<ref>Occasionally, publishers erroneously assign an ISBN to more than one title — the first edition of ''[[The Ultimate Alphabet]]'' and ''The Ultimate Alphabet Workbook'' have the same ISBN, 0-8050-0076-3. Conversely, books are published with several ISBNs: A ''German'', second-language edition of ''[[Emil und die Detektive]]'' has the ISBNs 87-23-90157-8 ([[Denmark]]), 0-8219-1069-8 ([[United States]]), 91-21-15628-X ([[Sweden]]), 0-85048-548-7 ([[England]]) and 3-12-675495-3 ([[Germany]]).</ref><ref>In some cases, books sold only as sets share ISBNs. For example, the [[Vance Integral Edition]] used only 2 ISBNs for 44 books.</ref> numeric commercial [[book]] [[identifier]] based upon the 9-digit '''Standard Book Numbering (SBN)''' [[code]] created by Gordon Foster,  Emeritus Professor of Statistics at [[Trinity College, Dublin]],<ref>Gordon Fosters original 1966 report can be found at  [http://web.archive.org/web/20110430024722/http://www.informaticsdevelopmentinstitute.net/isbn.html Informaticsdevelopmentinstitute.net]</ref> for the booksellers and stationers [[W. H. Smith]] and others in 1965.<ref name="history">{{citation | url = http://www.isbn.org/standards/home/isbn/international/history.asp | title = History | publisher = ISBN.org}}.</ref>

The 10-digit ISBN format was developed by the [[International Organization for Standardization]] (ISO) and was published in 1970 as international standard ISO 2108.<ref name= "history"/> (However, the 9-digit SBN code was used in the [[United Kingdom]]  until 1974.) An SBN may be converted to an ISBN by prepending the digit '0'. Currently, the ISO [[TC 46/SC 9]] is responsible for the ISBN. The [[International Organization for Standardization|ISO]] on-line facility only refers back to 1978.<ref>{{citation | format = [[PDF]] | url = http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=6897 | title = ISO 2108:1978 | publisher = ISO}}.</ref>

Since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with [[Bookland]] [[European Article Number|EAN]]-13s.<ref>{{citation | url = http://www.lac-bac.gc.ca/iso/tc46sc9/isbn.htm | title = Frequently Asked Questions about the new ISBN standard from ISO | author = TC 46/SC 9 | publisher = LAC‐BAC | place = CA}}.</ref>

Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure; however, this can be rectified later.<ref>Bradley, Philip (1992). "{{PDFlink|[http://www.theindexer.org/files/18-1/18-1_025.pdf Book numbering: The importance of the ISBN]|245KB}}. ''The Indexer.'' '''18''' (1): 25&ndash;26.</ref>

A similar numeric identifier, the [[International Standard Serial Number]] (ISSN), identifies periodical publications such as [[magazine]]s.

==Overview==

An ISBN is assigned to each edition and variation (except reprintings) of a book, for example an ebook, a paperback, and a hardcover would each have a different ISBN.<ref>{{PDFlink|[http://www.isbn-international.org/pages/media/Usermanuals/ISBN%20Manual%202012%20-corr.pdf See paragraph 5.2 of ISBN Users' Manual International edition (2012)]|548&nbsp;KB}}</ref> 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:

[[File:ISBN Details.svg|thumb|The parts of a 10-digit ISBN and the corresponding EAN‑13 and barcode. Note the different check digits in each. The part of the EAN‑13 labeled "EAN" is the [[Bookland]] country code.]]

#for a 13-digit ISBN, a ''[[GS1]] prefix'': 978 or 979 (indicating the industry; in this case, 978 denotes book publishing)<ref name= hail>Hailman, Jack Parker (2008). ''Coding and redundancy: man-made and animal-evolved signals.'' Harvard University Press. P. 209. ISBN 978-0-674-02795-4.</ref>
#the ''group identifier'', (language-sharing country group)<ref>Some books have several codes in the first block: e.g. A. M. Yaglom's ''Correlation Theory...'', published by [[Springer Verlag]], has two ISBNs, 0-387-96331-6 and 3-540-96331-6. Though Springer's 387 and 540 codes are different for English (0) and German (3); the same item number 96331 produces the same check digit: 6. Springer uses 431 as their publisher code for Japanese (4) and 4-431-96331-? would also have check digit ? = 6.  Other Springer books in English have publisher code 817, and 0-817-96331-? would also get check digit ? = 6. This suggests special considerations were made for assigning Springer's publisher codes, as random assignments of different publisher codes would ''not'' lead the same item number to get the same check digit every time. Finding publisher codes for English and German, say, with this effect amounts to solving a linear equation in modular arithmetic.
</ref>
#the ''publisher code'',<ref name=reed>Reed, Kennette (2008). ''From Idea to Author: How to Become Successfully Published.'' KRA Publications. P. 47. ISBN 978-0-9713718-4-2.</ref>
#the ''item number'' (title of the book),<ref name=reed/> and
#a ''[[checksum]] character'' or [[check digit]].<ref name=reed/>

The ISBN separates its parts (''group'', ''publisher'', ''title'' and ''check digit'') with either a [[hyphen]] or a space. Other than the check digit, no part of the ISBN has a fixed number of digits.<ref>The international ISBN agency's ''ISBN User's Manual'' says: "The ten-digit number is divided into four parts of variable length, which must be separated clearly, by hyphens or spaces" although permitting their omission for internal data processing, as the [[prefix]] code ensures that no two codes begin the same way. If present, hyphens must be correctly placed; see [http://www.isbn.org/standards/home/isbn/international/hyphenation-instructions.asp hyphenation instructions] at ISBN.org.</ref>

===ISBN issuance===

International Standard Book Numbers issuance is country-specific, and is tailored for each country's national goals. In Canada the stated purpose of issuing International Standard Book Numbers for no cost was to encourage Canadian culture. In the United Kingdom, United States, and other countries, the issuing of International Standard Book Numbers has become a profit center for the companies involved.

[[Australia]]: In Australia ISBNs are issued by the commercial library services agency [[Thorpe-Bowker]], and prices range from $40 for a single ISBN (plus a $55 registration fee for new publishers) through to $2,750 for a block of 1,000 ISBNs.<ref>{{Cite web
  | title = Bowker -- ISBN
  | publisher = Thorpe-Bowker  | date = Jan 5, 2009
  | url = http://www.thorpe.com.au/en-AU/products/servident_isbn.shtml
  | accessdate = March 29, 2012}}</ref> 

[[Canada]]: In Canada [[Library and Archives Canada]], a government agency, is the responsible entity, and there is no cost.

[[Pakistan]]: [[National Library of Pakistan]]<ref>National Library of Pakistan</ref> is responsible for ISBN registrations for Pakistani Publishers, Authors, Universities, Institutions and Government Departments who are responsible for publishing books.

[[India]]: In India, Raja Rammohan National Agency for ISBN is responsible for registration of Indian Publishers, Authors, Universities, Institutions and Government Departments who are responsible for publishing books.

[[United Kingdom]] and [[Ireland]]: In the United Kingdom and Ireland the privately held company, [[Nielsen Book Services]], part of [[Nielsen Holdings|Nielsen Holdings N.V.]], is the responsible entity, and there is a charge. ISBNs are sold in lots of ten or more.

[[United States]]: In the United States the privately held company [[R. R. Bowker]] is the responsible entity, and there is a charge, which varies depending upon the number of ISBNs purchased, with prices ranging from $125.00 for a single number.<ref>{{Cite web
  | last = Friedlander | first = Joel
  | title = Bowker's Andy Weissberg on ISBN and the Future
  | publisher = The Book Designer  | date = May 19, 2010
  | url = http://www.thebookdesigner.com/2010/05/bowkers-andy-weissberg-on-isbns-and-the-future-of-the-book/
  | accessdate = February 12, 2011}}</ref> 

Publishers and authors in other countries need to obtain ISBNs from their local ISBN Agency. A directory of ISBN Agencies is available on the [[International ISBN Agency]] website.

===Group identifier===

The [[list of ISBN identifier groups|group identifier]] is a 1 to 5 digit number. The single digit group identifiers are: 0 or 1 for [[English language|English]]-speaking countries; 2 for [[French language|French]]-speaking countries; 3 for [[German language|German]]-speaking countries; 4 for [[Japan]]; 5 for [[Russian language|Russian]]-speaking countries, 7 for [[People's Republic of China]]. An example 5 digit group identifier is 99936, for [[Bhutan]]. The allocated group IDs are: 0–5, 600–617, 7, 80–94, 950–989, 9927–9989, and 99901–99967.<ref>See [http://www.isbn-international.org/page/ranges a complete list of group identifiers].  ISBN.org sometimes calls them ''group numbers''. Their table of identifiers now refers to ''ISBN prefix ranges,'' which must be assumed to be group identifier ranges.</ref> Some catalogs include books that were published with no ISBN but add a non-standard number with an as-yet unallocated 5-digit group such as 99985; this practice is not part of the standard. Books published in rare languages typically have longer group identifiers.<ref name=hail/>

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]].

===Publisher code===

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 is it necessary for a book to display its number (except in [[People's Republic of China|China]]; {{clarify span|see below|reason=No mention of mandatory display in China further down in entry|date=December 2012}}). 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 ([[Euro|€]]558, [[United States dollar|US$]]915.46). The web site of the ISBN agency does not offer any free method of looking up publisher codes.<ref>See [http://www.isbn-international.org/page/directory Publisher's International ISBN Directory]</ref> Partial lists have been compiled (from library catalogs) for the English-language groups: [[List of group-0 ISBN publisher codes|identifier 0]] and [[List of group-1 ISBN publisher codes|identifier 1]].

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 has few digits allocated for the publisher number and many digits allocated for titles; likewise countries publishing much have few allocated digits for the group identifier, and many for the publishers and titles.<ref>Splane, Lily (2002). ''The Book Book: A Complete Guide to Creating a Book on Your Computer.'' Anaphase II Publishing. p. 37. ISBN 978-0-945962-14-4.</ref> Here are some sample ISBN-10 codes, illustrating block length variations.
:{| class="wikitable" width="100%"
! ISBN || Country or area || Publisher
|-
| <tt>99921-58-10-7</tt><!--ISBN-13: 978-99921-58-10-4--> || Qatar || NCCAH, Doha
|-
| <tt>9971-5-0210-0</tt><!--ISBN-13: 978-9971-5-0210-2--> || Singapore || World Scientific
|-
| <tt>960-425-059-0</tt><!--ISBN-13: 978-960-425-059-2--> || Greece || Sigma Publications
|-
| <tt>80-902734-1-6</tt><!--ISBN-13: 978-80-902734-1-2--> || Czech Republic; Slovakia || Taita Publishers
|-
| <tt>85-359-0277-5</tt><!--ISBN-13: 978-80-902734-1-2--> || Brazil || Companhia das Letras
|-
| <tt>1-84356-028-3</tt><!--ISBN-13: 978-0-14-015098-8--> || English-speaking area || Simon Wallenberg Press
|-
| <tt>0-684-84328-5</tt><!--ISBN-13: 978-0-684-84328-5--> || English-speaking area || Scribner
|-
| <tt>0-8044-2957-X</tt><!--ISBN-13: 978-0-8044-2957-3--> || English-speaking area || Frederick Ungar
|-
| <tt>0-85131-041-9</tt><!--ISBN-13: 978-0-85131-041-1--> || English-speaking area || J. A. Allen & Co.
|-
| <tt>0-943396-04-2</tt><!--ISBN-13: 978-0-943396-04-0--> || English-speaking area || Willmann–Bell
|-
| <tt>0-9752298-0-X</tt><!--ISBN-13: 978-0-9752298-0-4--> || English-speaking area || KT Publishing
|}

====Pattern====
English-language publisher codes follow a systematic pattern, which allows their length to be easily determined, as follows:<ref>[http://www.isbn.org/standards/home/isbn/international/hyphenation-instructions.asp Hyphenation Instructions]. ISBN.org.</ref>

{| class="wikitable" style="text-align:right;"
! rowspan="2" | Item number length
! colspan="3" | 0- group identifier
! colspan="3" | 1- group identifier
! rowspan="2" | Total
|-
! From !! To !! Publishers !! From !! To !! Publishers
|-
! 6 digits
| style="font-family:monospace;" | 0-00-xxxxxx-x
| style="font-family:monospace;" | 0-19-xxxxxx-x
| 20
| style="font-family:monospace;" | 1-00-xxxxxx-x
| style="font-family:monospace;" | 1-09-xxxxxx-x
| 10
| 30
|-
! 5 digits
| style="font-family:monospace;" | 0-200-xxxxx-x
| style="font-family:monospace;" | 0-699-xxxxx-x
| 500
| style="font-family:monospace;" | 1-100-xxxxx-x
| style="font-family:monospace;" | 1-399-xxxxx-x
| 300
| 800
|-
! 4 digits
| style="font-family:monospace;" | 0-7000-xxxx-x
| style="font-family:monospace;" | 0-8499-xxxx-x
| 1,500
| style="font-family:monospace;" | 1-4000-xxxx-x
| style="font-family:monospace;" | 1-5499-xxxx-x
| 1,500
| 3,000
|-
! 3 digits
| style="font-family:monospace;" | 0-85000-xxx-x
| style="font-family:monospace;" | 0-89999-xxx-x
| 5,000
| style="font-family:monospace;" | 1-55000-xxx-x
| style="font-family:monospace;" | 1-86979-xxx-x
| 31,980
| 36,980
|-
! 2 digits
| style="font-family:monospace;" | 0-900000-xx-x
| style="font-family:monospace;" | 0-949999-xx-x
| 50,000
| style="font-family:monospace;" | 1-869800-xx-x
| style="font-family:monospace;" | 1-998999-xx-x
| 129,200
| 179,200
|-
! 1 digit
| style="font-family:monospace;" | 0-9500000-x-x
| style="font-family:monospace;" | 0-9999999-x-x
| 500,000
| style="font-family:monospace;" | 1-9990000-x-x
| style="font-family:monospace;" | 1-9999999-x-x
| 10,000
| 510,000
|-
! colspan="3" style="text-align:right;" | Total
| 557,020
! colspan="2" style="text-align:right;" | Total
| 172,990
| 730,010
|}

==Check digits==
A [[check digit]] is a form of redundancy check used for [[error detection]], the decimal equivalent of a binary [[checksum]].  It consists of a single digit computed from the other digits in the message.

===ISBN-10 check digit calculation===
The 2001 edition of the official manual of the [http://www.isbn-international.org/ International ISBN Agency] says that the ISBN-10 [[check digit]]<ref>[http://www.isbn.org/standards/home/isbn/international/html/usm4.htm]</ref>&nbsp;– which is the last digit of the ten-digit ISBN&nbsp;– must range from 0 to 10 (the symbol X is used instead of 10) and must be such that the sum of all the ten digits, each multiplied by the integer weight, descending from 10 to 1, is a multiple of the number 11. [[Modular arithmetic]] is convenient for calculating the check digit using modulus 11. Each of the first nine digits of the ten-digit ISBN&nbsp;– excluding the check digit, itself&nbsp;– is multiplied by a number in a sequence from 10 to 2, and the remainder of the sum, with respect to 11, is computed. The resulting remainder, plus the check digit, must equal 11; therefore, the check digit is 11 minus the remainder of the sum of the products.

For example, the check digit for an ISBN-10 of 0-306-40615-''?'' is calculated as follows:
:<math>
\begin{align}
 s &= (0\times 10) + (3\times 9) + (0\times 8) + (6\times 7) + (4\times 6) + (0\times 5) + (6\times 4) + (1\times 3) + (5\times 2) \\
   &=    0 + 27 +   0 +  42 +  24 +   0 + 24  +   3 + 10 \\
   &= 130 = 12\times 11 - 2
\end{align}
</math>

Thus the check digit is 2, and the complete sequence is <nowiki>ISBN 0-306-40615-2</nowiki>.

Formally, the check digit calculation is:
:<math>(10x_1 + 9x_2 + 8x_3 + 7x_4 + 6x_5 + 5x_6 + 4x_7 + 3x_8 + 2x_9 + x_{10})\mod{11} \equiv 0. </math>

The value <math>x_{10}</math> required to satisfy this condition might be 10; if so, 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.
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.<ref>For example ''I'saka: a sketch grammar of a language of north-central New Guinea.'' Pacific Linguistics. ISBN "0-85883-554-4".</ref>

====Alternative calculation====
<source lang="php">
//PHP
function is_isbn_10_valid($ISBN10){
    if(strlen($ISBN10) != 10)
        return false;
	
    $a = 0;
    for($i = 0; $i < 10; $i++){
        if ($ISBN10[$i] == "X"){
            $a += 10*intval(10-$i);
        } else {//running the loop
            $a += intval($ISBN10[$i]) * intval(10-$i);
        }
    }
    return ($a % 11 == 0);
}</source>
<source lang="python">
#Python
def is_isbn10(isbn10):
    if len(isbn10) != 10:
        return False
    r = sum((10 - i) * (int(x) if x != 'X' else 10) for i, x in enumerate(isbn10))
    return r % 11 == 0
</source>
<source lang="ruby">
#Ruby
def is_valid?(isbn)
  (isbn.length == 10) && (isbn.split('').inject([10,0]){|a, c| i,s = a; [s+i*c.to_i,i-1]}.first%11==0)
end
</source>

===ISBN-13 check digit calculation===
The 2005 edition of the International ISBN Agency's official manual<ref>{{PDFlink|[http://www.isbn-international.org/en/download/2005%20ISBN%20Users%27%20Manual%20International%20Edition.pdf ISBN Users' Manual International edition (2005)]|284&nbsp;KB}}</ref> covering some ISBNs issued from January 2007, describes how the 13-digit ISBN [[check digit]] is calculated.

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 [[modular arithmetic|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:
<!-- This is what we'd like to do, but it is far too wide.
:<math>\textstyle \begin{array}{rlllllllllllll}
s &{}= 1 \times 9 &{}+ 3 \times 7 &{}+ 1 \times 8 &{}+ 3 \times 0 &{}+ 1 \times 3 &{}+ 3 \times 0 &{}+ 1 \times 6 &{}+ 3 \times 4 &{}+ 1 \times 0 &{}+ 3 \times 6 &{}+ 1 \times 1 &{}+ 3 \times 5 \\
 &{}= 9 &{}+21 &{}+ 8 &{}+ 0 &{}+ 3 &{}+ 0 &{}+ 6 &{}+ 12 &{}+ 0 &{}+ 18 &{}+ 1 &{}+ 15 \\
 &{}= 93
\end{array}</math>
-->
 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
 93 / 10 = 9 remainder 3
 10 –  3 = 7

Thus, the check digit is 7, and the complete sequence is <nowiki>ISBN 978-0-306-40615-7</nowiki>.

Formally, the ISBN-13 check digit calculation is:
:<math>x_{13} = \big(10 - \big(x_1 + 3x_2 + x_3 + 3x_4 + \cdots + x_{11} + 3x_{12}\big) \,\bmod\, 10\big) \,\bmod\, 10. </math>

This check system&nbsp;– similar to the [[Universal Product Code|UPC]] check digit formula&nbsp;– 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 number|prime]] modulus 11 which avoids this blind spot, but requires more than the digits 0-9 to express the check digit.

Additionally, if the sum of the 2nd, 4th, 6th, 8th, 10th, and 12th digits is tripled then added to the remaining digits (1st, 3rd, 5th, 7th, 9th, 11th, and 13th), the total will always be divisible by 10 (i.e., end in 0).

<source lang="java">
// Java
public static boolean isISBN13Valid(String isbn) {
    int check = 0;
    for (int i = 0; i < 12; i += 2) {
        check += Integer.valueOf(isbn.substring(i, i + 1));
    }
    for (int i = 1; i < 12; i += 2) {
        check += Integer.valueOf(isbn.substring(i, i + 1)) * 3;
    }
    check += Integer.valueOf(isbn.substring(12));
    return check % 10 == 0;
}
</source>
<source lang="javascript">
//JavaScript
function isValidISBN13(ISBNumber) {
    var check, i;
 
    ISBNumber = ISBNumber.replace(/-\s/g,'');

    check = 0;
    for (i = 0; i < 13; i += 2) {
      check += +ISBNumber[i];
    }
    for (i = 1; i < 12; i += 2){
      check += 3 * +ISBNumber[i];
    }
    return check % 10 === 0;
}</source>
<source lang="php">
//PHP
function is_isbn_13_valid($n){
    $check = 0;
    for ($i = 0; $i < 13; $i+=2) $check += substr($n, $i, 1);
    for ($i = 1; $i < 12; $i+=2) $check += 3 * substr($n, $i, 1);
    return $check % 10 == 0;
}</source>
<source lang="ruby">
# Ruby
def isbn_checksum(isbn_string)
  digits = isbn_string.split(//).map(&:to_i)
  transformed_digits = digits.each_with_index.map do |digit, digit_index|
    digit_index.modulo(2).zero? ? digit : digit*3
  end
  sum = transformed_digits.reduce(:+)
end

def is_valid_isbn13?(isbn13)
  checksum = isbn_checksum(isbn13)
  checksum.modulo(10).zero?
end

def isbn13_checksum_digit(isbn12)
  checksum = isbn_checksum(isbn12)
  10 - checksum.modulo(10)
end</source>

<source lang="python">
# Python
def is_valid_isbn13(isbn13):
    total = sum(int(num) * weight for num, weight in zip(isbn13, (1, 3) * 6))
    ck = (10 - total) % 10
    return ck == int(isbn13[-1])
</source>

<source lang="cpp">
// C/C++
bool is_valid_isbn13(char digits[13])
{
	int i, check=0;
	for (i=0; i<13; i+=2)
		check += digits[i];
	for (i=1; i<12; i+=2)
		check += 3*digits[i];
	return check%10==0;
}
</source>
<source lang="bash">
# Bourne-Again SHell
function is_valid_isbn13 () {
declare ISBN="${1//[^[:digit:]]}"
declare -i CheckDigit=0

  for i in $(seq 0 12); do
    CheckDigit+=$((${ISBN:$i:1}*(1 + 2*(i % 2))))
  done
  return $((CheckDigit % 10))
}
</source>

===Errors in usage===
Publishers and [[library|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.<ref>Lorimer, Rowland; Shoichet, Jillian; Maxwell, John W. (2005). ''Book Publishing I.'' CCSP Press. p. 299. ISBN 978-0-9738727-0-5.</ref>

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".<ref>[http://www.loc.gov/marc/bibliographic/bd020.html 020 - International Standard Book Number (R) &ndash; MARC 21 Bibliographic - Full]. Library of Congress.</ref> However, book-ordering systems such as [[Amazon.com]] will not search for a book if an invalid ISBN is entered to its search engine.{{Citation needed|date=March 2012}}

==EAN format used in barcodes, and upgrading==
Currently the [[barcode]]s on a book's back cover (or inside a mass-market [[paperback]] book's front cover) are [[European Article Number|EAN-13]]; they may have a separate barcode encoding five digits for the [[currency]] and the [[recommended retail price]].<ref>[http://www.barcodeisland.com/ean13.phtml EAN-13Methodology] — including a detailed description of the EAN13 format.</ref> The number "978", the [[Bookland]] "country code", is prefixed 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 an expected shortage in certain ISBN categories, the [[International Organization for Standardization]] (ISO) decided to migrate to a thirteen-digit ISBN (ISBN-13). The process began January 1, 2005 and was planned to conclude January 1, 2007.<ref>There is a [http://www.collectionscanada.ca/iso/tc46sc9/isbn.htm FAQ document] about this migration.</ref>  As of 2011, all the 13-digit ISBNs begin with 978.  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 [[Bookland|Musicland]] code for [[Sheet music|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, likewise, 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.<ref>[http://www.isbn.org/standards/home/isbn/transition.asp Are You Ready for ISBN-13?] at isbn.org.</ref>

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 [[bookstore|booksellers]] (e.g., [[Barnes & Noble]]) migrated to EAN barcodes as early as March 2005. Although many American and Canadian booksellers were able to read EAN-13 barcodes before 2005, most general retailers could not read them. The upgrading of the [[Universal Product Code|UPC]] [[barcode system]] to full EAN-13, in 2005, eased migration to the ISBN-13 in [[North America]].

==See also==
* [[Amazon Standard Identification Number|ASIN]] (Amazon Standard Identification Number)
* [[CODEN]] (serial publication identifier currently used by libraries; replaced by the ISSN for new works)
* [[Digital Object Identifier|DOI]] (Digital Object Identifier)
* [[English Short Title Catalogue|ESTC]] (English Short Title Catalogue)
* [[ETTN]] (Electronic Textbook Track Number)
* [[International Standard Audiovisual Number|ISAN]] (International Standard Audiovisual Number)
* [[International Standard Music Number|ISMN]] (International Standard Music Number)
* [[International Standard Musical Work Code|ISWC]] (International Standard Musical Work Code)
* [[International Standard Recording Code|ISRC]] (International Standard Recording Code)
* [[International Standard Serial Number|ISSN]] (International Standard Serial Number)
* [[ISWN]] (International Standard Wine Number)
* [[Library of Congress Control Number|LCCN]] (Library of Congress Control Number)
* [[List of group-0 ISBN publisher codes]]
* [[List of group-1 ISBN publisher codes]]
* [[Online Computer Library Center|OCLC]] number (Online Computer Library Center number [http://xisbn.worldcat.org/xisbnadmin/xoclcnum/index.htm])
* [[Registration authority]]
* [[Serial Item and Contribution Identifier|SICI]] (Serial Item and Contribution Identifier)
* [[Special:Booksources]], Wikipedia's ISBN search page
* [[VD 16]] (Verzeichnis der im deutschen Sprachbereich erschienenen Drucke des 16. Jahrhunderts)(in English: ''Bibliography of Books Printed in the German Speaking Countries of the Sixteenth Century'')
* [[VD 17]] (Verzeichnis der im deutschen Sprachraum erschienenen Drucke des 17. Jahrhunderts)(in English: ''Bibliography of Books Printed in the German Speaking Countries of the Seventeenth Century'')

==Notes==
{{Reflist|colwidth=30em}}

==External links==
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*[http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=36563&ICS1=1&ICS2=140&ICS3=20 ISO 2108:2005] at [http://www.iso.org www.iso.org]
* {{Cite web|title=Are You Ready for ISBN-13?|url=http://www.isbn.org/standards/home/isbn/transition.asp transition|publisher=R.R. Bowker LLC}}
* [http://www.bookweb.org/education/6865.html Description of the ISBN to EAN upgrade process] at bookweb.org
* [http://www.isbn-international.org International ISBN Agency]—coordinates and supervises the worldwide use of the ISBN system.
* [http://www.isbn-international.org/en/identifiers/allidentifiers.html Numerical List of Group Identifiers] List of language/region prefixes
* [http://www.isbn.org/converterpub.asp Free conversion tool: ISBN-10 to ISBN-13 & ISBN-13 to ISBN-10] from the [http://www.isbn.org/ ISBN agency]. Also shows correct hyphenation & verifies if ISBNs are valid or not.
* RFC 3187 <!-- should be automatically linked by Wikipedia --> Using International Standard Book Numbers as [[Uniform Resource Name]]s (URN)
* {{PDFlink|[http://isbn-international.org/en/download/implementation-guidelines-04.pdf Implementation guidelines]|51.0&nbsp;KB}} for the 13-digit ISBN code.
{{Audiovisual works|state=uncollapsed}}
{{ISO standards}}

[[Category:1966 introductions]]
[[Category:Book publishing]]
[[Category:Bookselling]]
[[Category:Book terminology]]
[[Category:Checksum algorithms]]
[[Category:Identifiers]]
[[Category:ISO standards]]
[[Category:Library science]]
[[Category:Universal identifiers]]

[[af:ISBN]]
[[ar:رقم دولي معياري للكتاب]]
[[as:আন্তৰ্জাতিক মান গ্ৰন্থ সংখ্যা]]
[[az:ISBN]]
[[bn:আন্তর্জাতিক মান পুস্তক সংখ্যা]]
[[be:Міжнародны стандартны кніжны нумар]]
[[bg:Международен стандартен номер на книга]]
[[br:ISBN]]
[[ca:ISBN]]
[[cs:International Standard Book Number]]
[[cy:Rhif Llyfr Safonol Rhyngwladol]]
[[da:Internationalt Standardbognummer]]
[[de:Internationale Standardbuchnummer]]
[[et:Rahvusvaheline raamatu standardnumber]]
[[el:Διεθνής πρότυπος αριθμός βιβλίου]]
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[[eu:International Standard Book Number]]
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[[fr:International Standard Book Number]]
[[fy:Ynternasjonaal Standert Boeknûmer]]
[[gl:ISBN]]
[[ko:국제 표준 도서 번호]]
[[hy:Գրքի միջազգային ստանդարտ համար]]
[[hi:आई॰ऍस॰बी॰ऍन॰]]
[[hr:Međunarodni standardni knjižni broj]]
[[ilo:Sangalubongan a Pagalagadan a Numero ti Libro]]
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[[mzn:شابک]]
[[ms:International Standard Book Number]]
[[nl:Internationaal Standaard Boeknummer]]
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[[pl:International Standard Book Number]]
[[pt:International Standard Book Number]]
[[ro:International Standard Serial Number]]
[[ru:Международный стандартный книжный номер]]
[[sco:International Standard Book Number]]
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[[simple:International Standard Book Number]]
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[[sl:Mednarodni sistem številčenja publikacij]]
[[szl:International Standard Book Number]]
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[[tl:Pandaigdigang Pamantayang Bilang ng Aklat]]
[[ta:பன்னாட்டுத் தரப்புத்தக எண்]]
[[th:เลขมาตรฐานสากลประจำหนังสือ]]
[[tr:ISBN]]
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[[ur:بین الاقوامی معیاری کتابی عدد]]
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[[zh:国际标准书号]]