DNA viruses have always been the most important model systems for eukaryotic DNA replication. Add to this the clinical significance of these human pathogens- 99% of the population of the world is infected with at least one of the viruses discussed in this volume (hepatitis B virus, Eptstein Barr virus or herpes simplex virus) - and it is difficult to overstate the importance of this group. What is clearly not possible is to summarize the enormous research effort involving these diverse viruses in a single volume and this is circumvented by concentrating on the theme of protein - protein interactions in DNA virus replication.