ISBN is for International Standard Book Number, issued by a select agency in the nation where the publisher resides. You’re probably familiar with 10 or 13 digit ISBNs appearing on the copyright page or above the barcode on the back of a print version book. The barcode just identifies the ISBN and may or may not include a price.

Even though ISBN is a number corresponding to a book, it has more to do with the publisher and edition than the title and author. For example, the same ebook could have several ISBNs for different retailers selling it, and it would need another ISBN for a paperback version and yet another for a hardcover or audio book. A separate version is needed for the ePub file compared to the mobi file. Or if you change the trim size of a paperback, like from 5 x 8 inches to 6 x 9…