Have you ever wondered where ISBNs (that 13-digit number and barcode) come from? An excellent source of information is the International ISBN Agency. Their FAQ page answers questions such as I am not a publisher; can I still obtain an ISBN? (The answer is Yes, by the way.) Links to the many national ISBN agencies are there, and quite a bit more info.
If you’re an author who is working on a digital version of an out-of-print or new book, of special interest is a PDF with the title Guidelines for the assignment of ISBNs to e-books. It answers questions such as If I publish in two or more different file formats (e.g. epub, PDF) should I assign separate ISBNs? and How can all the different versions of an e-book be linked together?
There is now a page on our blog called Indie Links where useful info about independent publishing of digital books will be found. Pages can be accessed using the green tabs along the top.