Thermal stress from cold and heat can affect health and productivity in a wide range of environmental and workload conditions. Health risks typically occur in the outer zones of heat and cold stress, but are also related to workload. Environmental factors related to thermal stress are reviewed. Individuals undergo thermoregulatory physiologic changes to adapt and these changes are reviewed. Heat and cold related illnesses are reviewed as well as their appropriate therapy. Published standards, thresholds and recommendations regarding work practices, personal protection and types of thermal loads are reviewed.