The International Civil Aviation Organization (ICAO) only accepted the original satellite navigation constellations (GPS and GLONASS) as a supplementary source of navigation data for civil air transport. This was not because of accuracy (although that is insufficient for some phases of flight), but because of the lack of integrity. Position errors due to a satellite fault, for example, can go undetected. This paper briefly summarises provisions specified by ICAO to make a trusted Global Navigation Satellite System, and looks forward to some new developments in providing trusted information to support the integrity of navigation solutions, which could also be used in other domains, e.g. autonomous vehicles.