ISBN (identifier)
History: The Standard Book Number (SBN) is a commercial system using nine-digit code numbers to identify books. In 1965, British bookseller and stationers WHSmith announced plans to implement a standard numbering system for its books. They hired consultants to work on their behalf, and the system was devised by Gordon Foster, emeritus professor of statistics at Trinity College Dublin. The International Organization for Standardization (ISO) Technical Committee on Documentation sought to adapt the British SBN for international use. The ISBN identification format was conceived in 1967 in the United Kingdom by David Whitaker (regarded as the "Father of the ISBN") and in 1968 in the United States by Emery Koltay (who later became director of the U.S. ISBN agency R. R. Bowker).
The 10-digit ISBN format was developed by the ISO and was published in 1970 as international standard ISO 2108. The United Kingdom continued to use the nine-digit SBN code until 1974. ISO has appointed the International ISBN Agency as the registration authority for ISBN worldwide and the ISBN Standard is developed under the control of ISO Technical Committee 46/Subcommittee 9 TC 46/SC 9. The ISO on-line facility only refers back to 1978.

An SBN may be converted to an ISBN by prefixing the digit "0". For example, the second edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has "SBN 340 01381 8", where "340" indicates the publisher, "01381" is the serial number assigned by the publisher, and "8" is the check digit. By prefixing a zero, this can be converted to ISBN 0-340-01381-8; the check digit does not need to be re-calculated. Some publishers, such as Ballantine Books, would sometimes use 12-digit SBNs where the last three digits indicated the price of the book; for example, Woodstock Handmade Houses had a 12-digit Standard Book Number of 345-24223-8-595 (valid SBN: 345-24223-8, ISBN: 0-345-24223-8), and it cost US$5.95.
Since 1 January 2007, ISBNs have contained thirteen digits, a format that is compatible with "Bookland" European Article Numbers, which have 13 digits.
The United States, with 3.9 million registered ISBNs in 2020, was by far the biggest user of the ISBN identifier in 2020, followed by the Republic of Korea (329,582), Germany (284,000), China (263,066), the UK (188,553) and Indonesia (144,793). Lifetime ISBNs registered in the United States are over 39 million as of 2020.

Overview: A separate ISBN is assigned to each edition and variation (except reprintings) of a publication. For example, an ebook, audiobook, paperback, and hardcover edition of the same book must each have a different ISBN assigned to it.: 12  The ISBN is thirteen digits long if assigned on or after 1 January 2007, and ten digits long if assigned before 2007. An International Standard Book Number consists of four parts (if it is a 10-digit ISBN) or five parts (for a 13-digit ISBN).
Section 5 of the International ISBN Agency's official user manual: 11  describes the structure of the 13-digit ISBN, as follows:

for a 13-digit ISBN, a prefix element – a GS1 prefix: so far 978 or 979 have been made available by GS1,
the registration group element (language-sharing country group, individual country or territory),
the registrant element,
the publication element, and
a checksum character or check digit.
A 13-digit ISBN can be separated into its parts (prefix element, registration group, registrant, publication and check digit), and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts (registration group, registrant, publication and check digit) of a 10-digit ISBN is also done with either hyphens or spaces. Figuring out how to correctly separate a given ISBN is complicated, because most of the parts do not use a fixed number of digits.

Issuing process: ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for that country or territory regardless of the publication language. The ranges of ISBNs assigned to any particular country are based on the publishing profile of the country concerned, and so the ranges will vary depending on the number of books and the number, type, and size of publishers that are active. Some ISBN registration agencies are based in national libraries or within ministries of culture and thus may receive direct funding from the government to support their services. In other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded.
A full directory of ISBN agencies is available on the International ISBN Agency website. A list for a few countries is given below:

Australia – Thorpe-Bowker
Brazil – The National Library of Brazil; (Up to 28 February 2020)
Brazil – Câmara Brasileira do Livro (From 1 March 2020)
Canada – English Library and Archives Canada, a government agency; French Bibliothèque et Archives nationales du Québec;
Colombia – Cámara Colombiana del Libro, an NGO
Hong Kong – Books Registration Office (BRO), under the Hong Kong Public Libraries
Iceland – Landsbókasafn (National and University Library of Iceland)
India – The Raja Rammohun Roy National Agency for ISBN (Book Promotion and Copyright Division), under Department of Higher Education, a constituent of the Ministry of Human Resource Development
Israel – The Israel Center for Libraries
Italy – EDISER srl, owned by Associazione Italiana Editori (Italian Publishers Association)
Kenya – National Library of Kenya
Latvia - Latvian ISBN Agency
Lebanon – Lebanese ISBN Agency
Maldives – The National Bureau of Classification (NBC)
Malta – The National Book Council (Maltese: Il-Kunsill Nazzjonali tal-Ktieb)
Morocco – The National Library of Morocco
New Zealand – The National Library of New Zealand
Nigeria – National Library of Nigeria
Pakistan – National Library of Pakistan
Philippines – National Library of the Philippines
South Africa – National Library of South Africa
Spain – Spanish ISBN Agency – Agencia del ISBN
Turkey – General Directorate of Libraries and Publications, a branch of the Ministry of Culture
United Kingdom and Republic of Ireland – Nielsen Book Services Ltd, part of NIQ
United States – R. R. Bowker

Registration group element: The ISBN registration group element is a 1-to-5-digit number that is valid within a single prefix element (i.e. one of 978 or 979),: 11  and can be separated between hyphens, such as "978-1-...". Registration groups have primarily been allocated within the 978 prefix element. The single-digit registration groups within the 978-prefix element are: 0 or 1 for English-speaking countries; 2 for French-speaking countries; 3 for German-speaking countries; 4 for Japan; 5 for Russian-speaking countries; and 7 for People's Republic of China. Example 5-digit registration groups are 99936 and 99980, for Bhutan. The allocated registration groups are: 0–5, 600–631, 65, 7, 80–94, 950–989, 9910–9989, and 99901–99993. Books published in rare languages typically have longer group elements.
Within the 979 prefix element, the registration group 0 is reserved for compatibility with International Standard Music Numbers (ISMNs), but such material is not actually assigned an ISBN. The registration groups within prefix element 979 that have been assigned are 8 for the United States of America, 10 for France, 11 for the Republic of Korea, and 12 for Italy.
The original 9-digit standard book number (SBN) had no registration group identifier, but prefixing a zero to a 9-digit SBN creates a valid 10-digit ISBN.

Registrant element: The national ISBN agency assigns the registrant element (cf. Category:ISBN agencies) and an accompanying series of ISBNs within that registrant element to the publisher; the publisher then allocates one of the ISBNs to each of its books. In most countries, a book publisher is not legally required to assign an ISBN, although most large bookstores only handle publications that have ISBNs assigned to them.
The International ISBN Agency maintains the details of over one million ISBN prefixes and publishers in the Global Register of Publishers. This database is freely searchable over the internet.
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 registration group identifier, several digits for the registrant, and a single digit for the publication element. Once that block of ISBNs is used, the publisher may receive another block of ISBNs, with a different registrant element. Consequently, a publisher may have different allotted registrant elements. There also may be more than one registration group identifier used in a country. This might occur once all the registrant elements from a particular registration group have been allocated to publishers.