The protein kinase family presents remarkable opportunities for drug discovery and development targeting mainly to the ATP binding cleft. Cyclindependent kinases CDKs control the cell division in by controlling its sub phases. The regulation of CDKs is altered in a number of tumor types, and therefore CDKs are a particularly attractive target group of kinases with reference to proliferative disorders including cancer, but also extending to graft stenosis, and autoimmune disorders. Screening of chemical modulators of CDKs that modulate aberrant CDK activity might be beneficial for cancer therapy by directly inhibiting kinase activity, or influencing cell cycle “checkpoint” function, which is mediated through effects of exogenous cellular regulators of CDK activity. In this regard small molecule modulators such as flavopiridol and UCN-01 are in early clinical trials. Other more selective modulators of CDK function are being actively sought, and initial results with flavopiridol analogs, indirubins, paullones, and purine-based inhibitors will be considered.