Cyclin-dependent kinases (CDKs) are core components of the cell cycle machinery that govern the transition between phases during cell cycle progression. Genes involved in cell cycle are frequently mutated in human cancer and deregulated CDK activity represents a hallmark of malignancy. This knowledge provides a rationale for regarding CDKs and their associated molecules as potential targets for new drug development in anticancer research. The present article will review the most relevant CDK inhibitors with emphasis on the newer molecules in clinical development and the biological rationale of this therapeutic approach.