Maithe, I've seen books with an N at the end of the ISBN number. You only put in the 10 or 13 digits so if the X makes longer than that, skip it. Also, ISBN numbers are not required on submissions, but I think it makes it easier for the validator if he or she has to look anything up or get a print copy of the book. I've never purchased an e-book so I couldn't say about ISBN numbers on those. I would presume they have them but since I don't have any e-books, I can't say for sure. That wouldn't matter for Bookshare anyway, since books have to be scanned to be allowed in Bookshare under the copyright exception, is my understanding. Jamie in Michigan Currently Reading - Lisey's Story - Stephen King