Chronic obstructive pulmonary disease (COPD) is a major health problem across the world and its medical, societal and economic impacts continue to grow. There are several hypotheses regarding the pathogenesis of COPD and important new information on airway inflammation, oxidative stress and proteolysis in the lungs that are important for the development of effective treatments. The differences in susceptibility to COPD among cigarette smokers and the common familial risk of developing disease point to important genetic influences. The identification of candidate gene loci and various gene polymorphisms have improved our understanding of the mechanisms by which genetic factors predispose for COPD. The beneficial effects of smoking cessation in slowing the decline in lung function and the progression of disease have been clearly established. Whether other factors such as mucus hypersecretion, respiratory infections and airway hyperreactivity contribute to disease progression independent of cigarette smoking is still being debated. There is new interest in dietary strategies to prevent or control COPD and preliminary information suggesting the usefulness of diets favoring antioxidant-rich foods. On the other hand several large, long-term, randomized, controlled clinical trials have failed to show a beneficial effect of either anticholinergics or corticosteroids in slowing the rate of decline in lung function in COPD. Corticosteroid treatment, however, appears to reduce the frequency of COPD exacerbations and there is some suggestion that it may also reduce the risk of death in patients with severe COPD.