The behaviour of a cell is defined by the set of genes it expresses and by its commitment to either a quiescent or a proliferating state. These processes are regulated by a family of enzymes called the cyclin-dependent protein kinases (CDKs). Our group studies CDKs that control both cell division and gene expression. We adopt a structure-based approach to understand how CDKs work, how they in turn are regulated, and how their inappropriate activity can contribute to the development of disease. In collaboration with our colleagues in the CRUK Drug Discovery Unit and elsewhere we develop potent and selective CDK inhibitors as probes to help understand CDK activity and as leads for drug design.