A great truth is a truth whose opposite. is also a great truth. Thomas Mann (Essay on Freud, 1937) This volume centers on pseudorabies (PR V), herpes simplex viruses 1 and 2 (HSV-1 and HSV-2), and human cytomegalovirus (CMV) and fulfills three objectives. The chapters on the epidemiology and latency of HSV, and on the glycoproteins specified by HSV and CMV, set the stage for the discussions of the immunobiology and pathogenesis of human herpesvirus infections in Volume 4. The epidemiology of HSV is the basis of our understanding of the spread and survival of this virus in the human populations. Central to the epidemiology of HSV and its pathogenesis in humans is the ability of the virus to remain in a latent state for the life of its host. The viral membrane glycoproteins are among the most interesting virion proteins, primarily because of their critical role in the initiation of infection. Since they are the surface membrane proteins of the virion and appear on the surface of productively infected cells, they are also the obvious if not the exclusive targets of the immune response. The chapters on the transforming potential of HSV and CMV, and on the role of HSV in human cancer, deal with challenging problems requiring rather different experimental tools.