As a result of the inefficiency of metabolic transfer, >75% of the energy that is generated by skeletal muscle substrate oxidation is liberated as heat. During exercise, several powerful physiological mechanisms of heat loss are activated to prevent an excessive rise in body core temperature. However, a hot and humid environment can significantly add to the challenge that physical exercise imposes on the human thermoregulatory system, as heat exchange between body and environment is substantially impaired under these conditions. This can lead to serious performance decrements and an increased risk of developing heat illness. Fortunately, there are a number of strategies that athletes can use to prevent and/or reduce the dangers that are associated with exercise in the heat. In this regard, heat acclimatisation and nutritional intervention seem to be most effective. During heat acclimatisation, the temperature thresholds for both cutaneous vasodilation and the onset of sweating are lowered, which, in combination with plasma volume expansion, improve cardiovascular stability. Effective nutritional interventions include the optimisation of hydration status by the use of fluid replacement beverages. The latter should contain moderate amounts of glucose and sodium, which improve both water absorption and retention.