The suprachiasmatic nuclei (SCN) harbor the master circadian pacemaker in mammals which is responsible for control and coordination of circadian rhythms throughout the body. They are a paired structure in the hypothalamus, located just above the optic chiasm, consisting of approximately 20 000 neurons. Due to their specific properties, the SCN have a unique position within the circadian system. They are connected with retina and, therefore, they can directly receive information about changes in external light/dark cycle. The individual SCN neurons are independent autonomous circadian oscillators which are inter-connected in a communication network. This network allows the individual SCN oscillators to synchronize among each other and thus to increase the precision and robustness of the oscillations. This work is focused to summarize the knowledge on the structure and function of the SCN at the level of single cells, subpopulations of cells and the whole SCN. The specific goal of this work is a summary of the factors that determine their central role within the circadian system
