Free Flight (FF) would permit aircraft to fly preferred routes, and self-separate, with minimal ATC intervention. The controller would be expected to intervene tactically only as necessary to ensure separation. Based on the results of earlier experiments at the NLR, an enhanced ATC display was developed that incorporated airborne-derived conflict detection and resolution information. Trials with controllers demonstrated benefits in terms of monitoring time and performance, as well as in general acceptance. Two important issues were identified for future work: (1) FF training needs and (2) controller responses to abnormal system modes.