EGNOS is a satellite-based augmentation system that improves the accuracy of satellite navigation signals over Europe. The system consists of transponders aboard three geostationary satellites over the eastern Atlantic Ocean and Europe, linked to a network of about 40 ground stations and four control centres.

The EGNOS ground stations receive signals sent out by the US GPS satellites. Information on the accuracy and reliability of these signals is relayed to users via the geostationary satellite transponders. This allows them to determine their position to within two metres, compared with about 20 metres for GPS alone. The Open Service is provided free of charge.

EGNOS is the first pan-European navigation satellite system. It was developed as a joint project by ESA, the European Commission (EC) and Eurocontrol, the European Organisation for the Safety of Air Navigation.