Chronic obstructive pulmonary disease (COPD) is a disease state characterised by airflow obstruction that is not fully reversible and progressive. Symptoms, as cough, sputum production and dyspnoea, functional impairment and complications of COPD can all be explained on the basis of the underlying lung inflammation and the resulting pathology. The chronic airflow obstruction is caused by a mixture of small airway disease (obstructive bronchiolitis) and parenchymal destruction (emphysema). On one hand, chronic inflammation causes remodelling and narrowing of the small airways. On the other hand, destruction of the lung parenchyma, also by an inflammatory process, leads to the loss of alveolar attachments to the small airways and decreases lung elastic recoil. In turn, these changes reduce the ability of the airways to remain open during expiration.