Thermoregulation refers to different mechanisms which are used to maintain a constant body temperature. The purpose of this seminar was to explore animal classification based on their thermal physiology and most commonly used thermoregulation mechanisms within different groups. Animals are divided into ectotherms, whose body temperature depends on the environment, and endotherms, who produce heat using their own metabolism which provides them with opportunity to have body temperature significantly higher than that of the environment. Invertebrates, fishes, amphibians and reptiles are considered to be ectothermic. Their thermoregulatory mechanisms mostly come down to those behavioural, although there are some physiological ones such as producing heat by shivering muscles. Birds and mammals are endothermic and they have more complex and effective mechanisms for maintaining body temperature. Apart from classifying animals based on how they produce heat, we can group them considering constancy of the temperature of their bodies. We distinguish organisms with relatively constant body temperature (homeotherms) and those with variable temperature (poikilotherms).