Chronic obstructive pulmonary disease (COPD) is characterized by irreversible airway obstruction and lung impairment. The two most common conditions are chronic bronchitis and emphysema. Chronic bronchitis involves excessive mucus production due to smoking-induced airway inflammation. Emphysema is the abnormal enlargement of airspaces due to an imbalance between the protease elastase and its inhibitor. Symptoms include a productive cough, shortness of breath, and signs of pulmonary hypertension. Treatment involves smoking cessation, oxygen therapy, bronchodilators, steroids, and antibiotics for infections.