The European COST 296 Action Alain Bourdillon (1) and Bruno Zolesi (2) (1)IETR, Université de Rennes 1, UMR CNRS 6164, Campus de Beaulieu, Rennes, France (2) Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy The European COST 296 Action MIERS: Mitigation of Ionospheric Effects on Radio Systems involves 18 European countries and 7 non COST institutions. It is structured in 3 Working Groups: WG1: Ionospheric monitoring and modelling WG2: Advanced terrestrial systems WG3: Spaced based systems In this paper we will present an overview of the Action and the work actually in progress.