In case of a nuclear accident in Europe, the Real-time On-line Decision Support system for off-site emergency management in Europe (RODOS) provides consistent and comprehensive information on the present and future radiological situation, the extent and the benefits and drawbacks of emergency actions and countermeasures, and methodological support for taking decisions on emergency response strategies. Main users of the system are those responsible at local, regional, national and supra-national levels for off-site emergency management. The application of the system for training and exercises was a further important consideration in its development.