"ISBN stands for International Standard Book Number and is used to uniquely identify every book. To ensure your book conforms to professional book publishing standards you will need to get an ISBN Number for all the books you publish in various formats.
One of my book titles is called the Atlanta Music Industry Connection. If I published the book as a soft cover (paperback), hardcover, e-book and audio book I would need four different ISBN Numbers for each version of the book. Of course, any new editions or revisions for your books should have its' own ISBN Number. Retailers, wholesalers, distributors, libraries and readers may all refer to an ISBN Number when attempting to find a book title.
Your ISBN Number should be used to generate the barcode for your book. Your barcode should be placed on the bottom right hand corner on the back cover of your book. The price should either be embedded with the barcode or appear right above it. This has become the industry standard and makes it easy for book retailers, wholesalers, distributors and librarians to find pricing details. Take a look at your personal books, visit the local bookstore or library and see if what I am saying holds true for most books you check out." How to Self-Publish for Profit