Retroviruses and herpesviruses are two important human pathogens. Together, they occupy one of the most important places in modern Medical Virology. Coinfections of these two viruses in the same individuals are frequently observed, especially in patients afflicted with AIDS. Potential consequences of such interactions include the exacerbation of the disease, changing of the disease courses and the release of new viruses, etc. An understanding of the underlying mechanism is important, but, thus far, few insights have been gained. The present monograph, arranged in eight chapters, is intended to provide an updated and concise review of recent works regarding the molecular and cellular mechanisms of such interactions. The topics covered range from transcriptional regulation, receptor modulation, genetic recombination, to AIDS and oncogenesis. Human immunodeficiency virus, avian leukosis virus, reticuloendotheliosis virus, herpes simplex virus, cytomegalovirus, herpesvirus-6 and Marek's disease virus are among the viruses discussed. The contributing authors are among the leaders in this field and are responsible for many of the original discoveries presented. This should serve as a valuable research and teaching reference for both beginning and advanced researchers in virology and oncology.