Human physiology is well adapted to sea-level atmospheric pressure. Decreased atmospheric pressures at altitude have profound effects on human physiology and anesthetic delivery. Seemingly arcane, the need for high-altitude anesthesia and critical care in disaster response is unusually common. The seismology and meteorology of high-altitude mountainous environments leads to frequent natural disasters. Approximately 140 000 000 people worldwide live persistently at altitudes above 2500 meters (8000 feet). Additionally, millions of people transiently visit high altitudes for vacation hiking, skiing, sport climbing, or other recreational pleasures. These endemic and visiting populations are subject to the risks of natural disasters, in addition to their usual needs for surgical care at elevation. Anesthesiology providers are also asked to support military operations, aviation, mountain-climbing expeditions, and disaster-response humanitarian missions at extreme altitudes. These latter operations may be conducted in minimally developed areas with limited resources and involve high-risk behaviors, trauma, minimal time for acclimatization, and hostile environmental exposure.