This is an information page. It is not a Wikipedia policy or guideline; rather, its purpose is to explain certain aspects of Wikipedia's norms or practices. It may reflect varying levels of consensus.

Shortcut H:ISBNH:ISBN

Many Wikipedia articles have an International Standard Book Number (ISBN) alongside the bibliographical entry for each book. Clicking on the linked 10- or 13-digit number links to WP:Book sources. This shows whether the particular book is listed in a library catalogue, at WorldCat, at Google Books, at major booksellers, or at other websites.

An example of a bibliographical entry as a reference or a suggestion for further reading would look like this:

• Carr, Edward Hallett (1972). What is History?: The George Macauley Trevelyan Lectures Delivered in the University of Cambridge, January–March 1961. Harmondsworth; Ringwood: Penguin Books. ISBN 0-14-020652-3.

The ISBN might lack hyphens between the digits, or it might contain spaces between the digits. Either way it should provide the link to WP:Book sources. Note that different editions of the same book may have different ISBNs. Also, books published prior to the 1970s do not have ISBNs, unless subsequently reprinted.

• Special:BookSources is the page to which each ISBN links. It links to many sources for a book throughout the world. You can also manually enter an ISBN – but you should click the linked ISBN to WP:Verify that the link is good.
• Category:International Standard Book Number includes all Wikipedia articles and templates directly related to ISBNs.
• Use {{ISBN}} to add an ISBN to an article, or |isbn= inside {{cite book}} and similar citation templates. Wikipedia:ISBN describes in detail how to add an ISBN to an article.

• International ISBN Agency – coordinates and supervises the worldwide use of the ISBN system.
• Conversion tool: ISBN-10 to ISBN-13 and ISBN-13 to ISBN-10 from the ISBN agency. Also shows verifies correct hyphenation and whether an ISBN is valid or not.