[en] As Caesium-137 is one of the main radionuclides which propagated over nearly the whole Europe by atmospheric transport and resulted in the contamination of the environment after the Chernobyl accident, and is now the only one to be detectable, this document reports the establishment of a mapping of this contamination in France and in some locations in Europe, thirty years after the accident. This study is notably based on a large collaboration and participation of citizens. After some recalls about the accident, and an indication of sampling locations, it presents the three types of samples: environmental indicators, food products and fungi (fungi can be considered as both environmental indicators and food products). Results are then presented and discussed with respect to soils (contamination is still present), to fungi (80 per cent of samples are contaminated), and to food products (fruits and vegetables are almost spared, but game is exposed due to its food and life environment, notably in Scandinavia for reindeers)