The hot/cold system is perhaps the most widely known medical belief system in the world. I propose that the wide acceptance of hot/cold ideas is due to the fact that they provide a particularly simple, economic coding for common human experience, such as hypothermia, heatstroke, and fevers. Coding of foods as heating or cooling can be understood in terms of a system of sensory cues that make the foods appear hot or cold. This paper deals primarily with data from Chinese culture.