Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8, and human T-cell lymphotrophic virus are viruses that are implicated in lymphoid neoplasia in humans. Their association with specific subsets of lymphomas suggests that they play an important, although not sufficient, etiologic role in their development. Current knowledge suggests that these viruses contribute to lymphomagenesis by subverting the host-cell molecular machinery to deregulate cell growth and survival. In this article, the basic information and recent developments that have contributed to our understanding of viral lymphomagenesis are reviewed.