The “Glossary of Terms for Thermal Physiology” provides useful definitions of the terms control and regulation. In the 1990s, evidence was raised that sympathetic nerve fibres control both vascular skin responses to thermal stimuli, vasodilation in case of heat load and vasoconstriction in case of heat loss. One is to modify the heat transfer to the environment by changing the thermal resistance and/or heat dissipation, the other is increasing or decreasing heat production. Research in the 1970s reported that some neurons of the mesencephalic reticular formation exhibit a high thermal sensitivity. 8% of these neurons can be considered as cold primary detectors and 79% as warm primary detectors, whereas the remaining 13% are interneurons. Specified threshold temperatures for certain thermo-effectors may change during the processes of fever, acclimatization and adaptation. Threshold temperature and thermo-effector gain are the dominant parameters describing the thermo-effector output as a function of body temperature, thus, they constitute essential characteristics of the thermal controller.