The cyclin dependent kinases, Cdks, are potential targets for new anticancer therapy. Dysregulation of the cell cycle is common during tumorigenesis, and inhibition of certain Cdks has been shown to inhibit tumor cell growth, induce apoptosis and cause tumor regressions in animal models. This review discusses the rationale for inhibiting Cdks as an approach to cancer therapy and the status of Cdk inhibitors in clinical trials. Compounds resulting from a patent literature search from 2003 to July, 2005 are discussed.