Environmental factors, such as cigarette smoking, outdoor and indoor pollution, and childhood respiratory infections, are believed to play a major role as risk factors for developing chronic obstructive pulmonary disease (COPD). The only confirmed genetic risk factor for COPD is the inherited deficiency of alpha 1-proteinase inhibitor. However, the evidence of familial clustering of lung function and COPD occurrence and the development of COPD among susceptible smokers, at variance with the so-called resistant smokers, would suggest that the weight of genetic risk factors is greater than recognized. In this paper the role of candidate genes for increasing the risk of COPD (such as alpha 1-proteinase inhibitor, alpha 1-antichymotrypsin, cystic fibrosis transmembrane conductance regulator, and others) is reviewed.