The purpose of this report is to present the 2006 version of the heat wave and health alert system. The basis of this system remains the same as that used during its first summer of operation in 2004 and improved in 2005, namely an alert issued when two biometeorological indicators simultaneously reach or exceed their respective thresholds, taking into account certain qualitative criteria (meteorological, environmental, social). These indicators are the three-day moving averages of minimum (IBMn) and maximum (IBMx) temperatures, and the corresponding thresholds are defined for each department with the aim of identifying potentially risky days. Changes to the warning system in 2006 primarily concern the practical aspects of the system’s organization. This report begins with a summary of the scientific foundations of the Heat Wave and Health Warning System (SACS). The various aspects of the evaluation of the heat wave warning system are then presented (external evaluations in 2004 and 2005, European workshop, internal evaluations, work of the DGS-InVS and InVS-Météo-France working groups), along with the improvements they have led to. Organizational aspects are discussed, particularly regarding the decision-making process, the information provided by Météo-France, the collection and analysis of mortality and morbidity indicators by the CIREs, the relationships between partners (various departments and bodies of the InVS, DGS, and Météo-France), and a summary of the alert and information channels. The 2006 SACS is part of the new version of the National Heat Wave Plan, which is divided into three levels: seasonal monitoring, warnings and actions, and maximum mobilization. It is operational from June 1 to August 31 and involves continuous interaction between Météo-France, the InVS, the CIREs, and health authorities. (R.A.)