ISBN is the International Standard Book Number assigned to every book. ISBN is publisher specific.  ISBN has three main purposes: to identify your book within the trade, help track sales and provide essential information about your title. Each version of your e-book, whether in MOBI format or in EPUB format, will need to have its own ISBN number. This allows retail publishers to differentiate between the different formats of your ebook. Our publishing packages include two ISBN numbers one for MOBI format, Kindle, and one for the EPUB format, iPad and others. The ISBNs that we provide will associate your e-book with Protégé Publishing and Promotion or authors can provide their ISBNs.