The atmosphere is part of the environment with which the human organism is permanently confronted. Epidemiological research investigates the occurrence of effects on morbidity and mortality due to heat, cold, air pollution and changes in the weather. Concentrating on aspects of the environment relevant for medical questions, three major complexes of effects can be discriminated: the complex conditions of heat exchange, the direct biological effects of solar radiation, and air pollution. Biometeorological knowledge can serve to assess the atmospheric environment, and can also be of help in the field of preventive planning, to conserve and develop the climate as a natural resource with regard to man's health, well-being and performance.