A general approach for the efficient use of satellite orbits and the radio frequency spectrum. The protection of received signals, equipment capabilities, and pertinent systems considerations are reviewed before systematically examining the principal direct and scatter modes of interference. Careful coordination to achieve the full potential use of satellite orbits and spectrum can provide enormous capacities, far exceeding any current proposals. Intensive sharing of the spectrum by microwave and satellite relays to fixed terminals would not seriously limit or inconvenience either. Satellite down links for mobile and broadcast services can share, fully and intensively, the spectrum above VHF with terrestrial services without loss to either. Satellite down links for area coverage to small terminals deserve priority in the UHF band. Although the greatest potential spectrum capacity lies above 16 GHz, propagation factors dictate that the lower spectrum should be shared much more intensively before making use of the higher frequencies. 38 pp. Ref.