This chapter addresses the medical and public health implications of extreme heat events (EHEs) and the associated mortality and morbidity. It provides a background to understanding EHEs as disasters. Increasing global warming, urbanization, and population numbers require improvement in effective EHE planning and response activities. The long-established concept of the Urban Heat Island is pervasive in the American and the European literature on EHEs, and applies, to a lesser extent, to urban areas in developing countries. Urban EHE response planning has developed into a unique policy area with its own literature that is scattered among larger disciplines. It is supported by a growing public awareness constantly reinforced by heat wave alerts. The Chicago Heat Wave of 1995 was a relatively short, but intense event that resulted in deaths within vulnerable populations and damaged the reputation of the political system that was slow in recognizing and coping with its consequences.