Chronic obstructive pulmonary disease (COPD) is a chronic progressive disease, characterized by irreversible airflow limitation, with a partially reversible component. The pathological abnormalities of COPD are associated with lung inflammation, imbalances of proteinase and antiproteinase, and oxidative stress, which are induced by noxious particles and gases in susceptible individuals. The physiological changes of COPD are mucus hypersecretion, ciliary dysfunction, airflow limitation, pulmonary hyperinflation, gas exchange abnormalities, pulmonary hypertension, cor pulmonale and systemic effects. The airflow limitation principally results from an increase in the resistance of the small conducting airways and a decrease in pulmonary elastic recoil due to emphysematous lung destruction. This article provides a general overview of the pathophysiology of COPD.