The International Standard Book Number, more commonly known as an ISBN, is a numeric commercial book identifier unique to each book. Originally ten numbers long (prior to 2007), ISBNs are now comprised of 13 numbers.
While paperback and hardback books require ISBNs, ebooks do not as the primary purpose of the number is to identify the book in a commercial system. Ebooks are not commercial or physical items and are not tracked in the same manner. Therefore, authors usually only need one ISBN for the purpose of self-publishing.
How you attain that ISBN is up to you.
Option #1: Amazon KDP
Amazon KDP offers free ISBNs to all authors, no matter the subject matter or genre. The advantage of this is that authors do not have to spend hundreds of dollars purchasing ISBNs, nor do they have to go through Bowker’s tedious registration process. It is quick and easy to use. If you are going to promote your book(s) by linking it to the Amazon page, then this is a wise choice. This selection does not alter your ability to sell your books at brick-and-mortar establishments as all of Amazon KDP is a print-on-demand platform.
Conversely, the use of an Amazon KDP ISBN ties your book to the digital platform. Therefore, if you were looking to publish on IngramSpark or Lulu as well, you would be unable to since the ISBN belongs to Amazon.
Option #2: Bowker
The United States ISBN Agency is called Bowker. An ISBN ensures your book’s information will be stored in the Books in Print database. Once you set up an account with Bowker, your ISBNs will be added to your account to recognize you as the publisher of the book titles.
As of June 2021, Bowker charges the following:
ISBNs never expire. If at first you choose Amazon KDP’s free ISBN and then decide you wish to publish using a purchased ISBN, the correction can be made in your manuscript and on your author dashboard with Amazon KDP.
If you are looking to exclusively use Amazon KDP to sell your books, then you do not need to purchase BARCODES. Even if you purchase an ISBN from Bowker and publish using KDP, you do not need to purchase a barcode.
However, if you are taking your book to small printer or looking to submit it to another digital platform, then you will need both an ISBN and a BARCODE. As of June 2021, Bowker sells barcodes for $25. A barcode-ISBN combination is also being sold for $150.
Amazon KDP ISBN Bowker ISBN Bowker Barcodes