The circadian distribution of vigilance states and body temperature changes are tightly coupled. The increase in heat loss at the end of the day is associated with increased ease to fall asleep. Experimental data show that warming the skin or the brain can increase sleep propensity, sleep consolidation, and the duration of sleep. Anatomical and neurophysiological studies show that the pre-optic-anterior-hypothalamus (POAH) is the main integrator of sleep and thermoregulatory information. It integrates information on vigilance states, body temperature, and environmental temperature and influences vigilance states and body temperature in response. Animals that display daily torpor may be a valuable model to investigate the relationship between sleep and thermoregulation. During torpor these animals seem to apply similar strategies and physiological processes as humans during entrance into sleep, but in a more extreme way, providing an excellent opportunity to investigate these processes in more detail. More systematic investigations are needed to further our understanding of the relationship between sleep and thermoregulation, and may provide the basis to treat sleep disturbances with thermal strategies.