Chronic obstructive pulmonary disease (COPD) is a preventable and treatable disease that causes a large health and economic burden both in the US and around the world. Most of the risk factors for COPD are well known. These include smoking, occupational exposures to toxins and irritants, ambient air pollution, airway hyper-responsiveness, asthma, and genetic factors. Major medical organizations have agreed on a common definition of COPD, although newer measures, such as functional status or exercise capability, have emerged as important in determining the prognosis of COPD patients. In most of the world, COPD prevalence and mortality continue to increase.