Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) describe the phenomenon of sudden worsening in airway function and respiratory symptoms in patients with COPD. These exacerbations can range from self-limited diseases to episodes of florid respiratory failure requiring mechanical ventilation. The average patient with COPD experiences two such episodes annually, and they account for significant consumption of health care resources. Although bacterial infections are the most common causes of AECOPD, viral infections and environmental stresses are also implicated. AECOPD episodes can be triggered or complicated by other comorbidities, such as heart disease, other lung diseases (e.g., pulmonary emboli, aspiration, pneumothorax), or systemic processes. Pharmacologic management includes bronchodilators, corticosteroids, and antibiotics in most patients. Oxygen, physical therapy, mucolytics, and airway clearance devices may be useful in selected patients. In hypercapneic respiratory failure, noninvasive positive pressure ventilation may allow time for other therapies to work and thus avoid endotracheal intubation. If the patient requires invasive mechanical ventilation, the focus should be on avoiding ventilator-induced lung injury and minimizing intrinsic positive end-expiratory pressure. These may require limiting ventilation and "permissive hypercapnia." Although mild episodes of AECOPD are generally reversible, more severe forms of respiratory failure are associated with a substantial mortality and a prolonged period of disability in survivors.