Public health measures need to be implemented to prevent heat-related illness and mortality in the community and in institutions that care for elderly or vulnerable people. Heat health warning systems (HHWS) link public health actions to meteorological forecasts of dangerous weather. Such systems are being implemented in Europe in the absence of strong evidence of the effectiveness of specific measures in reducing heatwave mortality or morbidity. Passive dissemination of heat avoidance advice is likely to be ineffective given the current knowledge of high-risk groups. HHWS should be linked to the active identification and care of high-risk individuals. The systems require clear lines of responsibility for the multiple agencies involved (including the weather service, and the local health and social care agencies). Other health interventions are necessary in relation to improved housing, and the care of the elderly at home and vulnerable people in institutions. European countries need to learn from each other how to prepare for and effectively cope with heatwaves in the future. Including evaluation criteria in the design of heatwave early warning systems will help ensure effective and efficient system operation.