Disasters are emergencies of a severity and magnitude resulting in deaths, injuries, illness and/or property damage that cannot be effectively managed by the application of routine procedures or resources. These events are caused by nature, the result of technological or manmade error. Natural disasters include typhoon, flood, heavy snowfall, drought, famine, and earthquake. Natural disasters are unpreventable and, for the most part, uncontrollable. Technological or manmade disasters include fire, nuclear accidents, bombings, and bioterrorism. The severity of damage caused by natural or technological disasters is affected by population density in disaster-prone areas, local building codes, community preparedness, and the use of public safety announcements and education on how to respond correctly at the first signs of danger. Recovery following a disaster varies according to the public's access to pertinent information, pre-existing conditions that increase or reduce vulnerability, prior experience with stressful situations, and availability of sufficient savings and insurance. Epidemiology can be used to investigate the public health and medical consequences of disasters. The aim of disaster epidemiology is to ascertain strategies for the prevention of both acute and chronic health events. Disaster epidemiology includes rapid needs assessment, disease control strategies, assessment of the availability and use of health services, surveillance systems for both descriptive and analytic investigations of disease and injury, and research on risk factors contributing to disease, injury, or death. With both disasters and the number of people affected by such events on the increase, the importance of disasters as a public health program is now widely recognized in Korea. The epidemiologists must do their best effort for prevention of disasters.