Environmental heat load is a major factor influencing performance. Numerous studies have looked at the impact of different environmental components on athletic functioning. Temperature, Humidity, Solar Radiation and Wind interact as stressors, impacting the athletes’ strain and performance. Repeated exposure to heat leads to one of the strongest forms of adaptation known, and reduces strain in the vast majority of exercisers. Various adaptation regimes have been evaluated. More recently, the question has arisen whether heat adaptation also has benefits that extend to exercise in cool conditions. This talk will try to provide an overview of some of these issues.