In January 1967 the Centre National d'Etudes Spatiales and the Secrétariat Général à l'Aviation Civile agreed on the definition of the main characteristics of the Project Dioscures, a system for telecommunications, air traffic control and navigation by means of satellites. Since then, technical studies have been carried out and the main equipment is being developed. The proposed system will enable air traffic control centres to provide continuous position determination for aircraft in the common visibility zone of two geostationary satellites. Furthermore, it will establish dependable and good-quality communication links between aircraft, control centres and other users (airlines and shipping companies, meteorological services, &c.). The system will initially be implemented over the Atlantic, mainly to serve the North Atlantic region, to be progressively expanded to cover the whole world.