[en] Smoking is the main environmental risk factor of COPD and accounts for 85% to 90% of COPD. However, 10-15% of COPD patients have never smoked and only a fraction of smokers ever develop COPD. Indeed, genetic and environmental (pollution, occupational and infectious) factors, also influence the risk of developing COPD. Finaly COPD must be considered as the clinical consequence of multiple complex interactions between environmental factors and genetic susceptibility. The latter is not clearly understood, with the exception of alpha-1 antitrypsin deficiency. In this article, we present the different aspects of this complex disease which is primarily environmental.