Man is not designed to live or to fight at altitude, and mountains have successfully resisted armies' attempts to conquer them for centuries. High-altitude mountainous terrain imposes great strains on individuals, units, and the health services designed to protect them. Medical personnel are challenged to minimize the damaging effects of the harsh environment, to maximize survival rates, and to preserve combat effectiveness by optimizing physiological and behavioral adaptation. Such challenges are best met with targeted medical training. This article reviews basic altitude physiology, relevant military history, the scope of altitude illnesses, prevention and treatment strategies, and existing mountain medicine training programs.