Humans are homeotherms and as such typically maintain a core body temperature of 37 ± 1°C. Environmental extremes in temperature challenge the homeostasis of the body, but our physiological systems have the capacity to adapt. Regular exposure to environmental temperatures greater than that normally experienced can lead to reductions in heart rate and core temperature, alongside increases in plasma volume and improvements in perception of effort. These adaptations can enable humans to be able to live, work and perform physical activity in hotter temperatures, it even enables humans to be able to run marathons in the desert. However, our ability for responding to these environments does have a limit and elevations of body temperature can be associated with heat illnesses. These illnesses lie on a continuum, the most severe being heat stroke which can prove fatal without immediate treatment. Global warming has resulted in a 0.8˚C – 0.9˚C increase in global mean temperature over the last century and projections predict further increases in temperature and heat wave frequencies. Heat waves are associated with increased heat illness hospital admissions and a rise in mortality rates. Consequently, this presentation will examine if humans have the capacity to cope with increased environmental temperatures, identify which populations and occupations may be at a greater risk, and discuss what interventions might be able to help.