The Director General of the French Institute for Public Health Surveillance provides an overview of the heat wave, a public health disaster that struck France in August 2003. His editorial introduces the articles in this special issue, which address: the measurement of excess mortality, determining factors, vulnerable groups... He raises questions concerning, in particular, prevention, the collection of morbidity and mortality data "in real time," better coordination among healthcare professionals and public health officials, and the necessary evolution of the warning system.