The long-term interest of my laboratory is to understand how the cellular genome is duplicated during the cell cycle. In the course of growth and division, eukaryotic cells duplicate their genomes with remarkable fidelity. The precision of this process depends in large measure upon stringent regulatory mechanisms that couple DNA replication to cell cycle progression. Initiation must be triggered at the appropriate time in the cell cycle at many hundreds or thousands of separate sites (origins of DNA replication) in the parental chromosomes. However, initiation must be prevented at these same sites in the newly synthesized daughter chromosomes. These controls ensure that each DNA segment in the genome is duplicated in a timely fashion exactly once each cell cycle.