Cell division and apoptosis are key aspects of cancer biology. The combination of increased cell proliferation and reduced cell death lies very close to the reason why cancer is a deadly disease. The importance of apoptosis and cell division in tumor biology has made them targets of new anti-cancer therapies. Although the cell division cycle and apoptosis might appear to be quite different from a physiological perspective and thus provide independent targets for therapy, recent evidence suggests that they are intertwined, and that an enzyme in one system might also have an important role in the other system. Protein kinase complexes known as cyclin-dependent kinases (Cdks) are the first example of such enzymes. In this review, we focus on the role of the subunits of different Cdks in both apoptosis and the cell cycle.