COPD is a complex syndrome causing pulmonary and systemic effects. The main feature is airway obstruction and the most important clinical phenotypes are chronic bronchitis and emphysema. COPD is characterized by high prevalence worldwide, relevant mortality and significant socio-economic burden. Pathogenetic mechanisms include epithelial damage, oxidative stress, inflammation, innate and adaptive immunity and remodeling. Predisposing factors are genetic background, age and lung growth/development. The main risk factor is tobacco smoke; other relevant risk factors are occupational exposure, environmental exposure to air pollution. COPD is a preventable disease and strategy to eliminate/reduce its risk factors have been applied successfully.