Tests of human endeavour have assessed exercise performance since the Ancient Greeks who visually inspected their Spartan athletes. Hot environments exacerbate the physiological demands of exercise, often leading to performance impairments and/or a risk of heat-related illness (HRI). Heat tolerance represents an individual’s ability to mitigate or avoid extreme body temperature elevations when exercising in hot environments. Heat tolerance tests have evaluated military personnel that have previously experienced an HRI. The choice of exercise performance tests within heat stress is comparable to those undertaken in temperate conditions, albeit requiring additional safety monitoring and data interpretation considerations. Practitioners are encouraged to match heat stress conditions of the expected environment and the sport demands during testing for accurate performance interpretation. Education also facilitates the athlete’s ownership and ‘buy-in’ for implementing testing. Consideration of scientific principles of all measures is necessary for accurate data interpretation during single or repeated heat stress testing.