The cell cycle in eukaryotes is a highly conserved, well-ordered series of events. During each cycle, DNA replication leads to the creation of two identical DNA molecules, which are compacted and structured for their segregation into daughter cells. In this section, we begin our discussion by reviewing the stages of the eukaryotic cell cycle, then introduce the master regulators, the cyclin-dependent kinases, and conclude with an overview of the principles that govern the cell cycle.