This post, by Ron Pramschufer, originally appeared on Publishing Basics on 3/14/11.
This is probably one of the most asked; least understood questions out there in the self-publishing world today. Technically you not only need an ISBN but you need a different ISBN for each format your ebook is being offered. If you are offering your book as a mobi, epub and a PDF, you need three different ISBNs. That’s technically. In reality, if you are only making your eBook available on Amazon, you don’t need any. Confused?
If you think about it a minute, it makes sense. If an ISBN is like a fingerprint, every different edition of your book needs a separate set of fingerprints (ISBN) to identify it. The easy one to understand is paperback and hardcover. They are obviously different editions. When a person purchases the paperback version of your book, that is what they expect to receive. The ISBN is what identifies the format. How about if the paperback book version was the tradebook size of 6 X 9. Let’s say you get an inquiry for the mass market paperback size of 4 ¼ X 7. Do you think you would need a new ISBN for the mass market size? Of course you would. How else would know which book was being ordered? So in reality, it is not one for the paperback version and one for the hardcover. It is one for each format. A 4 ¼ X 7 paperback is a different format from a 6 X 9 paperback, thus a different ISBN is needed.
Now let’s think about eBooks for a second. You need a separate ISBN for your eBook, right? Makes sense, doesn’t it? You wouldn’t want someone to order a paperback book when they really wanted an ebook. How do you tell the difference between the two? The ISBN, of course. Now let’s take that one step further. I want to buy an eBook to read on my Kindle. The file type that works on a Kindle is a Mobi file. I also want to buy the same book for my IPad. The IPad takes an ePub file. How do you think the store tells the difference between the two? What would happen if both versions has the same ISBN? It would be just like the trade paperback, mass market paperback situation. If it’s a different format, it needs a different ISBN. That’s the official story… Now the reality story for 99% of the self-publishers.
Amazon has its own numbering system called ASIN. The ASIN number for Publishing Basics-Navigating the Self-Publishing Minefield is B003Y8XR0K. Amazon uses the ISBN like window dressing. If you go to the eBook upload link at Amazon, the spot on the form that says ISBN, also says “Optional”. IE: You don’t need one for Amazon. Amazon is the only place that uses a Mobi file… Amazon has their own numbering system…therefore your Mobi file does not need a separate ISBN. Will the possible eBook formats remain at two? Fat chance. Do I suggest that you run out and buy a 100 block of ISBNs so you can be “ready”? NO. I suggest you purchase one and apply it to the ePub file.
Read the rest of the post, which includes a great deal more commentary and a lengthy Q&A section, on Publishing Basics.