A system is presented that allows the centralised real-time acquisition, analysis, and redistribution of the results produced by a community of atmospheric long-range transport and dispersion models. The models are used operationally by national authorities in different countries in Europe and around the world to forecast the long-range (100–2000 km) dispersion of accidental releases of radioactive material in the atmosphere. The ENSEMBLE system is conceived to allow decision makers and scientific advisors to decision makers to consult in real-time several atmospheric predictions produced during and after the release. The availability of several model predictions through the system allows collating several results into few concise representations and the use of the multi-model ensemble technique to determine the degree of agreement of model results in the absence of monitoring data. The paper presents the technical concepts behind the ENSEMBLE system, the methodology adopted to acquire several model predictions in real-time and to produce the multi-model analysis. Some examples of application to fictitious releases are also presented. ENSEMBLE has been specifically designed for the management of long-range atmospheric releases as a consequence of nuclear accidents but its concept is applicable to several other fields of environmental sciences.