What was learned from the extreme heat wave in Europe that occurred in summer 2003 causing 14 800 deaths in France and many more elsewhere? With the perspective of three years after the event, an emphasis is placed on the readiness of society in the case of a similar climatic event. Using 2003 recorded data and subsequent analyses, the paper addresses several components of social readiness for extreme heat waves: the thermal quality of the built environment at the scale of individual buildings as well the urban surroundings; the inhabitants' behaviour in managing indoor comfort; the consequences of clay soil subsidence; and the market boom for air-conditioning and the subsequent increased load placed upon the impaired capacity of the electricity supply system. These are specific instances of the following three general categories of climate impact: direct impacts on the population; impacts on the energy supply infrastructure; and impacts on buildings. Action plans that were proposed by several public authorities all aim at creating a better anticipation and coordination. The analysis of these decisions and their test during a heat wave in 2005 demonstrate the benefits of the integration of the proposed measures.