Chronic obstructive pulmonary disease (COPD) significantly reduces quality of life and is one of the main causes of chronic morbidity and mortality worldwide. Acute exacerbation of COPD (AECOPD) is a life-threatening condition that causes rapid deterioration of respiratory symptoms (worsening of dyspnea, cough and/or abundant sputum production) requiring urgent treatment. This review article examines the evidence underlying supplemental oxygen therapy and ventilator support during exacerbations of COPD. In the introduction, we discuss the epidemiology and pathophysiology of hypercapnic respiratory failure, and then we explain that the key to achieving appropriate levels of oxygenation is using controlled low-flow oxygen therapy. In patients with risk of hypercapnia a target oxygen saturation (SaO ) range of 88%–92% 2 is now generally accepted unless hypercapnia is disproved by gas analysis of arterial blood. However, if the partial pressure of carbon dioxide in arterial blood (PaCO ) is normal, oxygen therapy may target the usual saturation range of 94%–98%. 2 Many COPD patients may have a lower stable SaO , such that chasing this target (94%-98%) is not usually necessary unless 2 the patient is unwell. Further, we review current recommendations for ventilatory support in patients with AEHOBP. Noninvasive ventilation has assumed an important role in managing patients with acute respiratory failure. The use of invasive ventilation is the last remaining option, associated with a poor outcome.