This chapter provides students with an understanding of human thermoregulation, at rest and during exercise. It describes how the body adapts to repeated exposure in hot and cold environments. The chapter outlines practical exercises for the acquisition of techniques to monitor physiological responses to heat loads. Exercise implies activity of skeletal muscle and this demands energy. Most of the energy utilised is dissipated as heat, a small amount contributing towards mechanical work. The processes of conduction, convection, and radiation allow for either heat loss or heat gain with evaporation being a major avenue of heat loss when body temperature is rising. Body temperature is regulated by temperature-sensitive neurons located in the anterior and posterior hypothalamus. These cells detect the temperature of the circulating blood, with the cells in the anterior hypothalamus responding to an increase in body temperature and those in the posterior portion triggering the effector response to a decrease.