Only a few COPD phenotypes have been validated. They include α1-antitrypsin deficiency, frequent (two or more per year) exacerbations, chronic bronchitis, and upper lobe emphysema with poor exercise tolerance after rehabilitation in patients with severe airflow limitation. Other COPD phenotypes have been proposed, but still require validation confirming their relationship with clinically meaningful outcomes: severe hypoxaemia, disproportionate symptoms, persistent systemic inflammation, chronic airway bacterial colonisation, emphysema predominance with pulmonary hyperinflation and lung cancer, the asthma/ COPD overlap syndrome, premature or early severe airflow limitation (