Over the past four decades, a significant research effort has been devoted to the understanding of the epidemiology and pathophysiology of chronic obstructive airways disease (COPD) in adult life. Epidemiologic studies uniformly have identified cigarette smoking as the predominant risk factor for the occurrence of COPD. Other factors such as socioeconomic status, environmental pollution, occupational exposures, and inherent genetic susceptibility have been observed to have very limited roles as risk factors.