Every book version (paperback, hardcover, audio, eBook) needs an ISBN to sell. ISBNs should be purchased from Bowker, the only official place to buy your ISBNs. Other outlets have ISBNs for sale—some for cheaper—but they have caveats attached, and we do not recommend using them.
We recommend purchasing ten or more at a time because it is much less expensive in the long run. Each ISBN costs $125 with Bowker, and you will need one for your print book and one for your eBook, which will come to $250. If you purchase 10, the cost is $295, bringing your price down to $29.50 each! If you decide you want a hardcover or an audiobook, you’ll already have the ISBNs. Also, most authors plan on writing more than one book, so your ISBNs will be there ready for you when your next book is completed.
Here is the link to purchase your ISBNs: http://www.bowker.com/. Once you purchase your ISBNs, we can help you fill out the information Bowker will need for your books.