As part of the EC-financed RESTORE project ('Restoration of radioactively contaminated ecosystems'), an operational, user-friendly GIS-based Environmental Decision Support System (EDSS) has been developed. The RESTORE EDSS comprises a GIS-embedded modelling tool to assess the transfer of radiocaesium via food chains and external radiation exposures to humans based on an understanding of the nature of contamination, geo-chemical, hydrological, and biological processes, the different pathways for radiocaesium, and human behaviour. The EDSS accounts for spatial and temporal variation of these factors and is applicable to a variety of ecosystems. The overall aim of the EDSS is to identify vulnerable areas in terms of enhanced radionuclide transfer into food chains and/or the presence of 'critical population groups' that suffer enhanced internal and/or external exposure to radionuclides. Therefore, it provides information to support decisions about where to implement countermeasures and where to restore contaminated land most effectively. Predictions made by the EDSS use maps of soil contamination, soil type, and land use, production and production rates, and consumption habits of the affected population. The EDSS is illustrated by an analysis of the entire contaminated area of Ukraine, Belarus, and Russia.