The identification of risk factors is an important step toward developing strategies for prevention and treatment of any disease. The risks of COPD are related to environmental exposures in combination with the genetic makeup of the individual. The principal environmental factor in COPD is well known--exposure to cigarette smoke--and it can be modified. However, although smoking is the best-studied COPD risk factor, it is not only one. Air pollution, occupational dusts and chemicals can also cause COPD when the exposures are sufficiently intense or prolonged. This is a summary of environmental risk factors for COPD.