This thesis summarizes some aspects of COPD epidemiology in 2011. Prevalence of COPD is increasing worldwide. Even mild COPD is associated with worse outcomes when present in smokers or symptomatic subjects. In Switzerland, prevalence of moderate or severe COPD is lower than elsewhere. Beyond smoking, which is decreasing in developed countries, novel risk factors have been documented. In developing countries, biomass exposure probably constitutes the most important risk factor for COPD in women. In developed countries, the role of environmental risk factors such as air pollution or occupational exposure is to be considered. But, air pollution slowly decreased and heavy industries and mining activities are outsourced in developing countries. Risk factors such as asthma or bronchial hyper-responsivness do play a role. Both may be considered as the results of interaction between genes and environment.