n short, there is sufficient evidence that exposure to outdoor air pollution is a health hazard in China. The importance of these increased health risks is greater than in developed countries because air pollution in China is at much higher levels and because the Chinese population accounts for more than one-fourth of the world’s total population. Most of the Chinese studies discussed above were ecologic in nature, thus limiting their power for causal inference. Future research will need to clarify the lifetime course of air pollution effects with full control of potential confounders (e.g., prospective cohort studies), examine the relevance of cumulative exposures, disentangle effects of multiple pollutants, investigate gene–environment inter actions and other factors that may modify air pollution health effects, and identify pathophysiologic links between air pollution and health hazards for the Chinese population. Finally, pollution needs to be reduced and air quality and health indicators need to be monitored; this will enable the people and relevant authorities to be aware of the trends and consequences of air pollution, so they can determine how to ameliorate the situation.