The Medium Earth Orbit (MEO) region, home of the operational Global Navigation Satellite Systems (GNSS) GPS and Glonass, is becoming more and more exploited with the advent of the European Galileo and the Chinese Beidou constellations, both in their build-up phase. The sensitive applications of the navigation satellites and the absence of any natural sink mechanism, such as the atmospheric drag, call for a careful debris prevention policy able to preserve the MEO environment, avoiding in the future the problems now already faced by the LEO and the Geostationary Orbit (GEO) environments.