Should the e-book and print versions of my book have different ISBNs? If so, how are they linked over the Internet?

ISBN rules mandate that each different format has a different ISBN. That means, while hardcover and paperback versions are already issued different ISBNs, each ebook format (whether epub, pdf/a, mobi, or any other format) should also be issued a different ISBN.

Most retailing platforms will recognize the similarity between the various formats (versions) and link them together.