Dormancy is a phenomenon in which an animal temporarily slows down its metabolism, growth and development under unfavourable environmental conditions in order to conserve energy. There are different types of dormancy, such as torpor, which is used to temporarily slow down metabolism during periods of inactivity, long-term hibernation, which is used to avoid food scarcity and low temperatures in winter, aestivation, which is used to avoid high temperatures and drought in warm areas, brumation, which is used by cold-blooded reptiles at low temperatures, and diapause in arthropods, which completely halts development under unfavourable conditions. The answer to the question of how animals know when to enter dormancy and why they enter it at the same time each year or at the same stage of development lies in the study of biological rhythms. Many natural processes, such as the sleep-wake cycle, are inherently rhythmic and are controlled by an endogenous biological clock. This thesis describes different types of biological rhythms and clocks, the types of dormancy and the current knowledge about their correlation.