isbn

The International Standard Book Number (ISBN) is a numeric identifier used to uniquely identify books and related products in the publishing supply chain. An ISBN is assigned to each edition and format of a book by a publisher or a designated national agency and allows for efficient cataloging, ordering, and inventory management.

The ISBN system was introduced in the late 1960s and standardized as a 10-digit code in 1970. Since 2007, books are assigned 13-digit ISBNs based on the EAN-13 barcode system. Most 10-digit ISBNs can be converted by prefixing 978 and recalculating the check digit; new publications use 13 digits from the outset. The 13-digit form begins with a three-digit GS1 prefix, typically 978 or 979, followed by a country or language group identifier, a publisher identifier, an item number, and a final check digit.

The check digit uses a modulo 11 algorithm for ISBN-10, with the last digit possibly X, and a modulo 10 algorithm with alternating weights 1 and 3 for ISBN-13. The exact lengths of the group and publisher segments vary by country and publisher, so the total length may range from 10 to 13 digits historically; in modern practice, 13 digits are standard.

ISBNs are assigned by national ISBN agencies acting under the International ISBN Agency. They are primarily used by publishers, booksellers, libraries, cataloging systems, and distributors to identify titles and editions, facilitate data sharing, and streamline ordering and sales reporting.