Think of the ISBN as a serial number for your book. Unlike book titles and author names, the ISBN is always unique. Details of the book, such as size, pages, type of bind, author, publisher, etc are associated with the ISBN. We encourage authors to get their own ISBN, as it is free and easy to do in Canada. If you have no plan to put the book into the retail market there’s no need to even have an ISBN. The EAN barcode for a book will be created from the ISBN and is a simple process that should cost you next to nothing. So, don’t spend hundreds on one from unscrupulous web services!
For more information visit the Author’s Toolkit.