What an ISBN is
An International Standard Book Number identifies one edition of one book in the book trade's databases. The paperback, the hardcover, and the ebook are separate editions and would each carry their own number. It is a catalogue number, not a copyright and not a requirement for publishing.
When you need one
- Kindle ebook on KDP: no. Amazon assigns an ASIN and does not require an ISBN for Kindle editions.
- Paperback or hardcover on KDP: yes. KDP will supply a free ISBN, or you can bring your own.
- Other ebook stores and aggregators: some assign their own identifier, some ask for an ISBN. Check each one.
- Bookshops, libraries, and distributors: yes, always; an ISBN is how they order.
Free ISBN or your own?
The free KDP ISBN costs nothing and takes seconds, but KDP is recorded as the publisher of that edition and the number can only be used on Amazon's print platform. Your own ISBN lists you or your imprint as the publisher and travels with the book to any printer or distributor. If you plan to sell only on Amazon, the free one is fine. If you want bookshop or library orders, or you are building an imprint, buy your own.
Where ISBNs come from
- United States: Bowker, sold singly or in blocks; blocks are far cheaper per number.
- United Kingdom and Ireland: Nielsen.
- Canada: free from Library and Archives Canada for Canadian publishers.
- Other countries have their own national agency; the International ISBN Agency lists them.
An ISBN goes on the copyright page and inside the barcode on the back cover. KDP generates and prints the barcode itself; leave the box on your cover empty.