Individuals may seek the advice of medical providers when considering travel to high altitude. This article provides a basic framework for counseling and evaluating such patients. After defining “high altitude” and describing the key environmental features at higher elevations, the physiologic changes that occur at high altitude and how these changes are experienced by the traveler are discussed. Clinical features and strategies for prevention and treatment of the main forms of acute altitude illness are outlined, and frameworks for approaching the common clinical scenarios that may be encountered regarding high-altitude travelers are provided.