According to experts from the IPCC (Intergovernmental Panel on Climate Change), global warming is already underway, and its impact on health is one of the new priorities of the Executive Board of the WHO (World Health Organization). A specific resolution was thus adopted in January 2008. It is primarily recent major weather disturbances (heat waves and cyclones) that are, in France (metropolitan and overseas territories, respectively), the most notable climate change events for the media. Each of these climate-related hazards has, or will have, the potential for negative health effects, as indicated by the CDC (Centers for Disease Control and Prevention, a U.S. federal agency). However, its health effects will be both highly variable depending on the region and the specific climate phenomenon, and complex to identify because they occur across varying scales of time and space. Climate change can pose hazards by directly altering the environment (water, air, soil) or indirectly through floods and/or pollution (soil, sediments). These factors may lead to varying degrees of potential degradation in the quality of water intended for human consumption and recreational use, food, air quality (ozone, particulate matter, pollen, etc.), living conditions (temperature, precipitation, ultraviolet radiation, etc.), and the quality of the built environment. The selection of construction sites based on their vulnerability to flood and high-water risks, as well as the increasing urban density—which exposes a growing population to the same hazards (heat islands, sewage system overflows, etc.) will become mandatory parameters to consider in 21st-century civil and urban engineering and national land-use planning. Although the globalization of the economy and transportation contributes significantly to the large-scale spread of vector species and infectious agents, climate change will also play a role by creating environmental conditions favorable to their establishment and development. Significant changes are also to be expected in the microbial activity of aquatic and terrestrial ecosystems, disrupting the functioning of biogeochemical cycles. Related short-term effects, such as population aging, rising precariousness, and economic decline, risk amplifying the impact on public health by compounding the effects of climate change. Other collateral effects, such as varying levels of local healthcare availability across different regions of the country, may act as either a favorable or unfavorable factor in managing conditions associated with certain climate hazards. Examples include the need for ophthalmologists to treat cataracts and AMD (age-related macular degeneration) associated with longer exposure to ultraviolet rays, and for psychologists and psychiatrists to address post-disaster stress following exceptional events (such as floods). Furthermore, healthcare and medical-social facilities will also be exposed to extreme weather events (floods, storms), which in some cases may necessitate the relocation of people (e.g., elderly residents in nursing homes). Finally, spontaneous population displacement from high-risk areas to less exposed areas cannot be ruled out, both within mainland France (from Mediterranean areas to coastal areas) and in our Overseas Communities and Regions (from areas affected by cyclones to sheltered areas, for example). Such movements may have a positive impact on health, although it is difficult to assess this, but they will have economic and social consequences whose full extent we do not yet fully grasp. Similarly, individual behaviors in daily life (outdoor leisure activities and exposure to ultraviolet radiation or heatstroke, etc.) may change, leading to an underestimation of their public health costs. The effects of climate change on health depend on multiple risk factors, which most often interact with one another in chains of cause and effect, thus making their analysis and prediction complex. (Introduction)