This article presents the results of a study on the knowledge, attitudes, and behaviors of the French population regarding heat waves. The survey was conducted face-to-face with a representative sample of the French population aged 15 and older. The sample of 1,270 people was selected using the quota method. An oversample allowed for the inclusion of 302 people aged 75 and older. The results indicate that 94% of French people know that older adults are at risk during heat waves, but only 35% know that people with chronic illnesses are at risk. The need to “drink frequently and in large quantities” is cited less often by those aged 75 and older (65%) than by younger people (80%). People aged 75 and older took preventive measures significantly more often than younger people, such as avoiding going outside during the hottest hours of the day (54% versus 30%) or spending 2 to 3 hours in a cool place (37% versus 23%). Wetting the skin (body temperature regulation through water evaporation on the skin) was rarely mentioned and was rarely practiced by the general population, regardless of age, during the summer of 2005. It is necessary to improve information for those aged 75 and older regarding drinking during hot weather to prevent dehydration and to recommend to the general population (especially those aged 75 and older) the use of the cooling method involving water evaporation on the skin (wetting the skin and letting it dry).