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.

What does an ISBN identify?

ISBNs are assigned to text-based monographic publications (i.e. one-off publications rather than journals, newspapers, or other types of serials). Any book made publicly available, whether for sale or on a gratis basis, can be identified by ISBN. In addition, individual sections (such as chapters) of books or issues or articles from journals, periodicals, or serials made available separately may also use the ISBN as an identifier. Concerning the various media available, it is of no importance in what form the content is documented and distributed; however, each different product form (e.g. paperback, EPUB, .pdf) should be identified separately.