The role of cyclin-dependent kinases (CDKs) in regulating the transition of cell cycle steps makes this class of enzymes a suitable target for cancer therapy. Three different generations of CDKs inhibitors have been developed so far. Third-generation compounds (i.e. selective CDK4/6 inhibitors) are the most promising ones, due to their limited toxicity and high in vivo activity. To date, three compounds have entered the therapy, namely Palbociclib, Ribociclib and Abemaciclib. Herein we review the medicinal chemistry aspects of these drugs, with some references to very similar analogues that have been published.