Chronic Obstructive Pulmonary Disease (COPD) occurs frequently in elderly people, and is associated with episodes of worsening symptoms such as dyspnea, coughing and sputum (i.e. exacerbations). These COPD exacerbations sometimes require hospitalisation and increase the risk of mortality. We will perform epidemiologic research in large population-based cohort studies to unravel the clinical and genetic risk factors of COPD exacerbations.