Central sleep apnea (CSA) is characterized by the periodic occurrence of apnea caused by loss of ventilatory motor output. CSA is often discussed as a minor variant of obstructive sleep apnea.However, this view obscures the critical contribution of CSA as an important manifestation of breathing instability in a variety of conditions with diverse causes. Central apnea can also be a physiologic phenomenon in healthy people during sleep onset. Conversely, patients who have obstructive apnea may also develop episodes of apparent central apnea, and apneas that begin as central may become obstructive as respiratory effort is restored ("mixed apneas"). Thus, there is a significant overlap between obstructive and central apnea. This article addresses the pathophysiology, clinical features, and management of normocapnic and hypercapnic CSA.