It's nice that they ask, but I can't see that you're obligated to go along. You might note that there is no suggestion of any additional fees or royalties. Before you agree to this let me ask you -- would you have written the book originally for free? Bottom line, the publisher signed a contract with you and that existing contract is binding. It's unfortunate, for them, that they didn't anticipate electronic publishing, but that's hardly your problem. Professional writers get paid. End of story. Karl Bridges University of Vermont