Chronic obstructive pulmonary disease (COPD) continues to cause a heavy health and economic burden in the United States and around the world. Some of the risk factors for COPD are well known and include smoking, occupational exposures, air pollution, airway hyperresponsiveness, asthma, and certain genetic variations, although many questions remain, such as why < 20% of smokers develop substantial airway obstruction. There are several different definitions of COPD and the definitions depend on accurate diagnosis. Small differences in the definition can have large effects on the estimates of COPD in the population. In addition, newer measures, such as functional status or exercise capability, have emerged as important in determining the prognosis of COPD patients. Furthermore, evidence continues to emerge that COPD represents several different disease processes, with potentially different interventions required. In most of the world COPD prevalence and mortality are still increasing and will probably continue to rise in response to increases in smoking, particularly by women and adolescents. Resources aimed at smoking cessation and prevention, COPD education, early detection, and better treatment will be of the most benefit in our continuing efforts against this important cause of morbidity and mortality.