Critically ill patients have severe sleep disruption and typically encounter loss of circadian sleep pattern, steep fragmentation, increasing proportions of transitional stages of sleep, and loss of slow wave and rapid eye movement sleep. Mechanical ventilation is associated with these same sleep abnormalities, but what is attributable to the intensive care unit environment versus mechanical ventilation itself may be difficult to discern. Recent studies have shown that the ventilator mode and inappropriate settings can contribute to sleep fragmentation, and it is important to avoid overventilation that can induce central apneas when using spontaneous breathing modes. Noninvasive ventilation in the acute setting seems to be associated with the same sleep abnormalities as invasive ventilation. Long-term noninvasive positive pressure ventilation assists ventilation nocturnally and improves for patients with chronic respiratory failure caused by restrictive thoracic disorders.