The navigation and control of commercial aircraft has developed in an almost random fashion during the past forty years. Now circumstances have produced an opportunity, through the ICAO Special Committee on Future Air Navigation Systems, for the industry to put time aside from more immediate problems to plan ahead for the future. Although our current methods and procedures are immeasurably better than those of forty years ago there is now little scope for further refinement and it is very apparent that by the end of the century present systems will be unable to cope efficiently with the traffic in the world's high-density areas. In addition our current methods do not permit us to operate our aircraft as efficiently as we would wish.