Normal cell cycle progression is controlled by the sequential action of cyclin-dependent kinases (CDKs), the activity of which depends on their binding to regulatory partners (cyclins). Deregulation of cell cycle is one of the first steps that transform normal cells into tumor cells. Indeed, most cancer cells bear mutations in members of the pathways that control the CDK activity. For this reason, this kinase family is a crucial target for the development of new drugs for cancer therapy. Recently, both ATP-competitive CDK inhibitors and the last generation of non-ATP-competitive inhibitors are emerging as promising agents for targeted therapies. Many clinical trials are in progress, using CDK inhibitors both as single agents and in combination with traditional cytotoxic agents. In this review, we will discuss new therapeutic strategies based on the use of CDK inhibitors in cancer.