The summer of 2003 was the hottest France had experienced in 53 years. A heat wave of exceptional intensity occurred during the first half of August, with maximum and minimum temperatures significantly above seasonal norms. The August 2003 heat wave was accompanied by significant ozone pollution, both in terms of duration and intensity. Several epidemiological studies were urgently launched to assess the short-term health consequences of the heat wave. The cumulative number of excess deaths was approximately 14,800 between August 1 and 20, representing a 60% increase compared to expected mortality (Inserm study). Excess mortality affected all of France, even in departments where the number of heatwave days was low. This finding is corroborated by the “13 Cities” study. Overall, excess mortality affected cities more than their respective regions. These surveys also provided an initial description of the characteristics of those who died during the heat wave. They show that the elderly bore the heaviest toll and suggest that people with limited independence or suffering from a physical disability or mental illness were the most vulnerable to the heat. Data collected from other European countries confirm the health impact of various heat waves that occurred at different times and with varying intensities across Western Europe during the summer of 2003. It appears that France was the European country most severely affected by the heat wave. In order to compare the health impact of this exceptionally hot summer across different countries, harmonization of methods is essential, whether for defining exposure indicators or effect indicators. Ongoing collaboration among experts from different countries must be fostered through the development of international research programs. Given the scale of the health impact of the August 2003 heat wave in France, studies and initiatives in the areas of surveillance and early warning have been implemented. A partnership has been established with Météo France to develop an operational warning system, an integral part of a national action plan implemented by health authorities to address future heat waves. An analysis of historical meteorological and mortality data was conducted in 14 cities to define the most appropriate indicators and warning thresholds. An analysis of the role of air pollution in the health consequences of the 2003 heat wave will be conducted in the coming months as part of the PSAS 9 program. Epidemiological studies aimed at identifying risk factors for deaths at home and in care facilities linked to the heat wave are currently underway. The August 2003 heat wave had a major impact on public health in France. This event led to a reevaluation of our public health system’s ability to anticipate this type of crisis. The collaborations developed on this occasion and all the actions and studies implemented aim to inform the discussion on the implementation of effective prevention strategies. (R.A.)