Though they are easy to use and may be removed from most paper surfaces, DON'T be tempted to use them in books. These seemingly harmless "markers" leave behind their adhesive, even when removed immediately. The adhesive hardens and leaves a film that becomes acidic. This results in eventual discoloration and brittleness of the paper. They were designed for short-term application to expendable documents and have no place being used on permanent records and books.