There is no doubt that CDK/cyclin complexes play a central role in the regulation of the cell cycle. Many other components of the cell division cycle regulatory network have been identified recently. There is still much to be learned, however, about how these components cooperate to form this perfectly working mechanism. Many control points of the cell cycle regulatory mechanism are the same or similar across a wide range of eucaryotes. It is rather obvious that the cell division cycle is the most fundamental process for all living organisms. Still, there is no 'general' cell cycle. Individual regulatory mechanisms depend on the organism being studied and also on the developmental stage of cells within this organism.