Definition
International Standard Book Number — a unique 13-digit numeric identifier assigned to each edition and format of a published book. ISBNs are required for distribution through major retail channels including Amazon, bookstores, and libraries. For self-publishing creators, obtaining an ISBN (either through a self-publishing platform like KDP, which provides free ISBNs, or independently through a national ISBN agency) is a foundational step in establishing a book as a legitimate commercial publication. Owning your own ISBN — rather than using a platform-provided one — gives you greater control over distribution and publishing rights.