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Cyclin-dependent kinases (eng. cyclin-dependent kinases, CDK) is a group of proteins regulated by cyclin and cyclin-like molecules. Most cyclin-dependent kinases are involved in the change of phases of the cell cycle; they also regulate the transcription and processing of mRNA.

Cyclin-dependent kinases are serine / threonine kinases and phosphorylate the corresponding amino acid residues in proteins. There are several cyclin-dependent kinases, each of which is activated by one or more cyclins and other similar molecules after reaching their critical concentration. These enzymes are mostly homologous and differ primarily in the configuration of the binding site of cyclins. In response to a decrease in the intracellular concentration of a particular cyclin, a reversible inactivation of the corresponding CDK occurs. If cdks are activated by a group of cyclins, each of them, as if transferring protein kinases to each other, supports cdks in the activated state for a long time. Such CDK activation waves occur during the G1 and S phases of the cell cycle.