Once the organism has been invaded, all herpesviruses persist. This is accomplished by a change in the acute productive phase of the infection into the latent form. Reactivation of the latent virus ensures renewed transmissibility of the infection. This pathogenetic principle is ensured by an extremely finely tuned virus-host interrelationship which has developed in a unique specific manner for each herpesvirus. Pathogenetic fundamentals are discussed taking herpes simplex and the varicella-zoster virus as examples, and the resulting clinical consequences are shown.