During the early phase of a large-scale accident with release of radioactivity to the atmosphere, it is essential to notify and inform competent authorities as early and as extensively as possible. Only when the accident is rapidly notified and information is continuously made available in the form of real-time monitoring data and dispersion forecasts are decision makers able to define appropriate countermeasures. The Chernobyl accident taught us that information exchange should be carried out in a harmonised and consistent manner. Although several European countries already had developed automatic monitoring networks by 1986 and in some cases established bilateral agreements to exchange this information, the size of the accident demonstrated the need to extend such schemes to the continental scale. It became important to have commonly agreed international data formats and procedures in place. Over the past 25 years, the European Commission has invested in improving the rapid exchange of information and data in the event of a major accident. For the early phase of emergency support, it has focussed on three closely related systems: the early notification system ECURIE, the automatic data exchange platform EURDEP and the atmospheric dispersion model exchange and evaluation system ENSEMBLE. Starting from the legal background, we describe these information systems in detail with an emphasis on their current status and their planned future developments.