This paper presents a review of the use of the airspace and the air traffic control system. Safety, capacity and efficiency of this use under Visual Flight Rules (VFR) are compared with the evolving constraints imposed by operations under Instrument Flight Rules (IFR). The concept of Electronic Flight Rules (EFR) as developed by Topic Group III on Freedom of Airspace in the FAA’s 1978–79 E & D Initiatives Process is reviewed. The potential for conservation of air traffic control manpower and aircraft fuel is further developed. Promising areas for further technical exploration are noted. The paper concludes with some considerations for co-existence of VFR, IFR, and EFR traffic during a transition period.