Epstein-Barr virus (EBV), Kaposi’s sarcoma herpesvirus (KSHV), also called Human Herpesvirus 8 (HHV-8), and human T-cell lymphotrophic virus (HTLV-1) are viruses that are well documented to be causally associated with lymphoid neoplasia in humans. Other viruses have also been proposed to be involved in lymphomagenesis, but their role may be indirect, or the association is not well established. Current knowledge suggests that EBV, KSHV and HTLV-1 contribute to lymphomagenesis by subverting the host-cell molecular signaling machinery to deregulate cell growth and survival. It appears that de-regulation of the NF-ΚB pathway is a common strategy used by these three viruses to promote cell survival, thereby playing a critical role in tumorigenesis. The understanding of the mechanisms of viral carcinogenesis could lead to the identification of novel therapeutic targets and to the development of rationally designed therapies. In this chapter, the basic information and recent developments that have contributed to our understanding of viral lymphomagenesis, and its possible therapeutic implications are reviewed.