The prevalence of reported sleep disturbances in a general population is high. Many of the complaints are the result of sleep-related breathing disorders, due mainly to the occurrence of obstructive and central apnoeas. Obstructive sleep apnoea is a fully described and well-recognized entity. Central sleep apnoea (CSA) however, has been poorly studied. There is accumulating evidence that central sleep apnoea should be considered as the end of a spectrum. Instability in the breathing pattern is the main underlying mechanism and is due to the interaction of many factors. Breathing during sleep is dependent on metabolic control and the activity of the respiratory muscles. Decreased chemical drive and/or failing respiratory muscle function are associated with CSA and usually also with ongoing hypoventilation during wakefulness, characterized by chronic daytime hypercapnia. Central respiratory drive can also be inhibited by upper airway reflexes. Mostly, however, CSA occurs as the hallmark of unstable breathing during sleep brought about by an overall increase in loop gain (especially in light sleep stages) and the unmasking of a CO2 threshold. Arousal following central apnoeas acts as an amplification of the instability. Micro electroencephographic (EEG) arousals are often observed as a consequence of CSA. They are responsible for sleep fragmentation and hypersomnolence during the day. The daytime hypersomnolence and complaints of awakenings during sleep in patients with CSA can be striking. CSA can occur in specific pathologies, such as chronic heart failure and (post-traumatic) brain lesions, that are associated with irregular breathing. Treatment strategies are remarkably few in number. Use of nasal ventilation and the inhalation of CO2 are mainly of theoretical interest, since patients do not often tolerate these more invasive therapies. Drug treatment, especially with acetazolamide, is easier to perform. Stimulation of upper airway reflexes, by less invasive methods, seems to be promising for the near future.