It depends on whether your IDL 8.1 license has a current maintenance contract. If you do have a current maintenance contract, then you can upgrade the license to work with IDL 8.5 with no additional cost. If you do not, then you will probably need to purchase a new license. You can contact Harris Geospatial Solutions Tech Support (support@harris.com) or your local distributor directly to find out whether you have current maintenance. You will want to have your IDL license number ready. This number is shown as the Installation Number when you start a new IDL session. Regards, Peg