Chronic obstructive airway disease (COPD) is a major cause of disability, and it’s the third leading cause of death in the United States. It is a progressive condition characterized by exacerbations and remissions of coughing, mucus production, shortness of breath, wheezing, chest tightness, and other symptoms. Pathologically, COPD is manifested in emphysema and/or chronic bronchitis. The leading cause of COPD is tobacco smoking. However, emerging epidemiologic evidence suggests that long-term exposure to air pollution also contributes to the symptoms of COPD. While the disease is progressive, it develops slowly and the underlying mechanisms are unclear. This chapter investigates the role of air pollution in COPD and the cellular-molecular pathways of pollutant-caused pathological changes.