Amazon will assign an ISBN if you do not provide one. They will also arrange the barcode for your printed book. However, this ISBN cannot be used with other retailers and has Amazon as an imprint.
It might be better to get your ISBN if you plan to make your book available on retailers other than Amazon. The same ISBN can be used across all platforms.
How to get the ISBN?
ISBNs are usually issued by the national library or similar institution of each country; for US authors, the official authority is Bowker. A single ISBN costs $125, and there are discounts when ordering more ISBNs.
If you do not want to spend this amount of money, you can use the imprint of an established publisher by purchasing their book services.
Barcodes are only needed for printed books – the barcode shows the ISBN, as well as the price of the book and, is placed on the back cover.
If you want to be cost-effective and avoid spending hundreds of dollars on ISBNs, the most recommended way would be to work with a reputable self-publisher. And that would be with us. We’ve worked with over 500 authors publish their book to success, and our services are the certainly one of the best in the game (we really mean that).