The cell cycle covers cell proliferation and growth and is strictly regulated by cyclin-dependent kinase, cyclins and their inhibitors. Cyclin-dependent kinases are serine/threonine kinases that are activated in certain phases of the cell cycle by regulatory subunits, cyclins, with which they form functional heterodimeric complexes. Under physiological conditions, the activation of cyclin-dependent kinases and cyclins is strictly controlled. The formation of these complexes is inhibited, as needed, either specifically or non-specifically, by cyclin-dependent kinase inhibitors. Progression through the cell cycle is a critical process that drives many aspects of cellular function. The cell cycle is a series of events that occurs in a repeating pattern. Each cell cycle consists of two phases, interphase and mitotic phase. Their dysregulation leads to disruption of cell cycle coordination and uncontrollable cell proliferation, which is the main feature of tumorigenesis (Fig. 1, Ref. 69). Keywords: cell cycle, regulation, cyclin‑dependent kinases, cyclins, inhibitors.