In light of the significant health impact of the August 2003 heat wave, government authorities established a National Heat Wave Plan (PNC), which outlines the preventive measures and care protocols to be implemented in the event of a heat wave across the country. The activation of the PNC’s alert levels is based on a warning system developed by the Institute for Public Health Surveillance (InVS) and Météo France. This warning system alerts public authorities three days in advance of a potential heat wave. The Heat Wave and Health Alert System (SACS) is based on climate monitoring and the analysis of so-called "biometeorological" indicators at the departmental level. Thus, for each French department, temperature data and mortality rates from the past thirty years have been used to define alert thresholds based on biometeorological indices corresponding to three-day moving averages of temperatures forecast by Météo France. Alert thresholds, specific to each department, trigger a graduated response from the healthcare system—in terms of preventing heat-related illnesses and providing care for individuals—when these thresholds are exceeded (or are forecast to be exceeded). The benefit of this system is that it can predict the onset of a heat wave three days in advance, allowing preventive measures to be put in place before the heat wave sets in. In parallel with climate monitoring, the Regional Interregional Epidemiology Unit (Cire) is responsible for organizing, at the regional level, the collection of information to describe changes in the population’s health status in order to detect early the effects of heat on health, whether in terms of morbidity or mortality. This surveillance is intended to assess the health impact of the heat wave to better anticipate potential difficulties in providing care for people. Excess mortality or an increase in emergency department activity can trigger the National Heat Wave Plan’s (PNC) transition to the warning and action (MIGA) level and the activation of the white, red, blue, and vermilion plans. This report presents the system implemented by the Languedoc-Roussillon Regional Health Agency and describes the context of the various alerts in the region. A final section presents an analysis of the health impact of the heat wave from June 30 to August 1, 2006. (introduction)