Glossary
What is an ISBN?
An ISBN is a 13-digit number that identifies one specific edition of one specific book. Bookshops, libraries and distributors use it to order the right thing; it is a product code, not a copyright registration.
One number, one edition
The word doing the work is edition. A paperback and an ebook of the same book are two editions and take two ISBNs. A hardcover is a third. A second edition with a new chapter is a fourth. A reprint with a typo fixed is not — the content and format are the same, so the number stays.
Since 2007 an ISBN has been 13 digits. The older 10-digit numbers still exist on older stock and convert cleanly, which is why you sometimes see both printed on a copyright page.
When you actually need one
- Selling a print book through a shop, a library or a distributor. They order by ISBN. Without one you are not in the catalogue they order from.
- Selling a paperback through [print-on-demand](/glossary/print-on-demand). Every print-on-demand service requires an ISBN on the book, though most will give you one.
- Being findable in industry databases — Books in Print, Nielsen, and the national library systems that feed them.
When you don’t
An ebook sold only through Amazon does not need one. Amazon assigns its own identifier, the ASIN, and that is what its store runs on. The same is true of a PDF you sell from your own site or give away as a lead magnet — there is no catalogue for it to be in.
This is the single most common thing new authors overbuy. If your whole plan is “ebook, on Amazon”, you can publish without ever touching an ISBN.
Where they come from, and what they cost
ISBNs are issued per country by a national agency — Bowker in the United States, Nielsen in the UK, and a national library or agency almost everywhere else. In some countries, including Canada, they are free. In the United States they are not, and Bowker sells them far more cheaply in blocks than singly, which is the reason “buy 10, not 1” is the standard advice.
Amazon KDP will also give you a free ISBN for a paperback. The catch is real but narrow: a free KDP ISBN lists Amazon as the imprint and cannot be used to print the same book anywhere else. If you might ever print through a second service, buy your own.
Related terms
- ASINAn ASIN is the 10-character code Amazon assigns to every product in its catalogue, including books. It is Amazon’s own identifier — it works nowhere else, and Amazon creates it for you automatically.
- Print on demandPrint on demand means a single copy is printed and shipped only after a customer orders it. There is no print run, no minimum order and no box of unsold books in your hallway — you are paid the difference between the list price and the printing cost.
- Copyright pageThe copyright page is the page on the back of the title page carrying the copyright notice, the edition, the ISBN and any disclaimers. In most countries it creates no rights — copyright already exists — but it states plainly who owns what.
- Book metadataMetadata is everything about your book that is not the book itself: title, subtitle, author, description, categories, keywords, price and language. In a store with millions of titles, it is most of what decides whether yours is ever seen.
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