In July 2003 Europe experienced one of its most severe heat waves in recorded history. Beginning in mid-July and peaking around late July, exceptionally high temperatures persisted for several weeks across France, Spain, Portugal, Italy, Germany, the Netherlands, Belgium, Switzerland and parts of the United Kingdom and Eastern Europe. The heat wave coincided with unusually dry conditions and atmospheric patterns that trapped hot air over the continent, producing daytime temperatures well above seasonal norms and warm nights that prevented relief. France was the hardest hit in terms of documented excess mortality. Official national estimates and subsequent epidemiological studies attributed roughly 14,800 excess deaths in France during the heat wave period; other countries also recorded substantial excess mortality, bringing the Europe-wide total to tens of thousands by several assessments. Excess deaths were concentrated among older adults, people with pre-existing health conditions, and socially isolated individuals who lacked cooling or support. Mortality rose both from direct heat-related causes (heatstroke, dehydration) and from exacerbations of cardiovascular and respiratory illnesses. The crisis exposed vulnerabilities in public health systems and social care. Many hospitals and nursing homes lacked adequate air conditioning, and some care facilities failed to identify or assist residents at greatest risk. Emergency medical services and morgues faced increased demand. In several countries, comparisons of heat-related mortality led to national inquiries and reviews of institutional practices, particularly around care for the elderly. In the aftermath, governments and public health agencies introduced changes aimed at preventing a repeat catastrophe. France established a national heat-health action plan that included early warning systems, public advisories, temperature monitoring, outreach to vulnerable individuals, and protocols for hospitals and care homes. Other countries similarly developed or strengthened heatwave plans, emergency response coordination, and public education about heat risks. Urban planners and policymakers also emphasized long-term measures such as increasing green spaces and improving building design to reduce heat exposure. Scholars and public-health officials have cited the 2003 heat wave in broader discussions about climate change and extreme heat risk. While a single event cannot be ascribed solely to climate change, analyses indicate that warming trends increase the likelihood, intensity, and duration of extreme heat events, thereby raising future risk for heat-related mortality unless adaptation and mitigation measures are implemented. Historical assessments of the 2003 event rely on excess-mortality calculations, which compare observed deaths during the heat period with expected deaths based on prior years. These methods account for underreporting of heat-specific causes and reveal the full mortality impact of the event, although estimates vary by country depending on data quality and methodology. Beyond mortality, the heat wave had other measurable effects: reduced agricultural yields in some regions, stress on energy systems due to higher demand for cooling and hydropower reductions, and disruptions to transport and other services. The 2003 European heat wave remains a reference point for public-health preparedness and climate adaptation in Europe. It prompted concrete institutional changes in several countries and deepened scientific and policy attention to protecting vulnerable populations from extreme heat. Ongoing monitoring, early-warning systems, community outreach, and infrastructural adaptations are among the measures now emphasized to reduce the health toll of future heat extremes.