Epidemiological, clinical, and experimental evidence correlates current levels of ambient air pollution with both respiratory and cardiovascular effects. Oxidative stress, inflammation, induction of a pro-coagulatory state and dysfunction of the autonomic nervous system appear to play a major role. Acute effects include changes in lung function, heart rate, blood pressure and inflammatory state, and clinical measures such as respiratory symptoms, thrombosis, myocardial infarction, arrhythmia, stroke, and death. In addition, there is an increase in the use of health care resources due to these effects. Long-term consequences of cumulated exposure include adverse effects on lung growth, chronic bronchitis, lung cancer, and probably the development of asthma and atherosclerosis. These morbidities ultimately lead to shorter life expectancy. Host factors including genotype are important modifiers of the effects of air pollution. Further research will help identify susceptible subgroups and disentangle specific effects and mechanisms associated with various constituents and sources of air pollution.