The SurSaUD® syndromic surveillance system (Health Surveillance of Emergency Room Visits and Deaths) was established in 2004 by the French Institute for Public Health Surveillance (InVS) in the wake of the 2003 heat wave. This extreme weather event—which had severe consequences, including overburdened emergency services and excess mortality of nearly 15,000 deaths—demonstrated that the surveillance systems available at the time were unable to detect such a phenomenon or quickly assess its impact on the population. The Ministry of Health and the InVS then decided to establish a surveillance system that was both non-specific (not based on predefined pathologies) and reactive, with data reported in real time or near real time (daily transmission). (R.A.)