EXACO is a French prospective observational epidemiological study. Chest physicians will enrol 1200 patients who will be followed up for 4 years. The aims of the study are to describe the exacerbations in COPD patients at different levels of severity and to confirm the existence of a sub-group of patients defined as frequent exacerbators. The clinical characteristics associated with this profile and the decline of FEV1 will be evaluated. A validation of the VSRQ scale will be performed. The data will be collected from chest physicians and by phone calls to the patients every three months.