EBV is a B lymphotropic virus that is associated with a range of human malignancies. Although for many of these tumours the association has long been established, unraveling the precise role of EBV in disease pathogenesis has been more difficult. This review summarizes current knowledge concerning the association between EBV and human cancers and illustrates how an increasing appreciation of patterns of latent gene expression and latent gene function in different cell environments is already helping towards a better understanding of both the natural history of infection in normal individuals and how EBV contributes to malignant transformation. Finally, therapeutic strategies that target EBV in tumours are discussed.