One of the more interesting developments in herpesvirus evolution concerns the acquisition of novel, non-ubiquitous herpesvirus genes. A number of these are related to known cellular genes. How did herpesviruses acquire such genes? Our recent demonstration of retrovirus integration into herpesviruses suggests a potentially important role for retrotransposition in herpesvirus evolution and in the acquisition of novel genes, cellular in origin. Herpesvirus genome development has been characterized by a number of structural and evolutionary properties that support this proposal. We first discuss the evidence for retroviral integration into herpesviruses. The functional significance of this phenomenon is presently unclear. However, in the broader context of retrotransposition, a number of attractive features serve to explain the capture of structural and regulatory elements throughout herpesvirus evolution. These possibilities are discussed in detail.