Dear Gary, The x applies to a library edition. If you are lucky enough to be able to tell by the feel if your book is a library book or retired library book by a library address that may have scanned in the preliminary pages or by the cellophane over the dust jacket or a pocket glued inside or remnants of it, go with the x. Otherwise, go with the ISBN that ends with a number. I believe the inside text is the same for both so either ISBN won't hiccup the system. Evan speculates that when the check sum of the ISBN digits add up to a two digit number, the x is used for the last digit. He also suggests that you check on the back cover in case one ISBN is printed near the bottom edge in which case you could go with that one. Sometimes an ISBN is on the dust jacket flaps as well. I'll be interested to hear if anyone else has more info on this topic. I've proofed books with two ISBNs which aren't followed by paperback, hardcover or library edition in parenthesis. I've used the methods described above as well as copying the numbers into the Amazon search as Susan suggests to see which product description matches my book, to decide which number to use. As a proofer, when I check in a book, the Bookshare tools fill in an ISBN, especially a 13 digit ISBN to replace the 10 digit ISBN in my book. Then, the last digit is different anyway and I defer to the 13 digit number provided. I love being in the company of so many people who care enough to make sure all the i's are dotted and the t's are crossed! We are a class act! Always with love, Lissi ----- Original Message ----- From: Gary Petraccaro To: bksvol-discuss@xxxxxxxxxxxxx Sent: Tuesday, January 25, 2011 1:57 PM Subject: [bksvol-discuss] ISBN Problem I have a book with two different isbns. How do I find out which one applies? 0-517-348020 0-517-14641-X