The cell cycle kinase has been well-characterized and has also been well-exposed in numerous proceedings volumes and collections. In this issue of Advances in Molecular Cell Biology, the cell cycle kinase is ever present, but in the early chapters it has a supporting role. Center stage are the regulatory mechanisms that control the kinase. The contribution that the centrosome (the organelle of cell division) makes to cell cycle regulation are described. The part played by calcium and calcium-controlled regulatory proteins is emphasized. The importance of phosphatase as well as kinase activity to cell cycle regulation is stressed. The last words are reserved for the mitotic kinase: the last chapters describe its effects and its regulation in cell-free systems.