International Standard Book Number

The ISBN is a numerical book identifier intended to be unique. 

ISBNs were 10 digits in length up to the end of December 2006, but since 1 January 2007 they now always consist of 13 digits. ISBNs are calculated using a specific mathematical formula and include a check digit to validate the number.

An ISBN is assigned to each separate edition and variation (except reprints) of a publication. For example, an ebook, a paperback, and a hardcover edition of the same book will each have a different ISBN.

What is an ISBN used for?

An ISBN is essentially a product identifier used by publishers, booksellers, libraries, internet retailers and other supply chain participants for ordering, listing, sales records and stock control purposes. The ISBN identifies the registrant as well as the specific title, edition and format.