I propose to discuss the problem of long-range navigation from the point of view of the A.T.C. system planner and to describe in outline the work that has been done in the North Atlantic Systems Planning Group (N.A.T.S.P.G.). In this area there are tidal flows of traffic of relatively high density and there is inevitably a need to reduce separations as much as possible, consistent with safety, to ensure operating costs are reduced, or at least kept in bounds with anticipated increases in traffic. This requires a much more precise definition of an acceptable separation standard, and for future planning the establishment of a relationship between separation standards and navigational capability.