An ISBN is a 13-digit International Standard Book Number that uniquely identifies books and other book-like publications. The number identifies a single title or edition as a publication produced by a specific organization and is used by booksellers, wholesalers. libraries and distributors. A typical ISBN has five parts:

• The digits "978" which identify the current ISBN series;
• A country identity used by a national or geographic group of publishers;
• A publisher's identity;
• A title which identifies a specific publication or edition; and
• A single validation digit.

In most cases, an ISBN is translated into a bar code using an internationally agreed format. Many retailers require that books can be identified in this manner.

ISBNs are assigned by over 160 ISBN agencies, mostly on a national basis. A publisher purchases a block of ISBNs incorporating a unique publisher identity, and can then assign numbers from within the block to publications for which it holds the publishing rights.

Once an ISBN publisher prefix and associated block of numbers has been assigned to a publisher by the ISBN Agency, the publisher can assign ISBNs to publications it holds publishing rights to. The numbers cannot be re-sold or transferred to other publishers.