The widespread application of molecular virologic technology has resulted in a rapid expansion in our knowledge of the physical, biologic, and clinical properties of EBV. As data continue to accumulate, we may better understand the pathogenesis of, and more clearly define diseases associated with, primary and reactivated infection due to this virus. The development of new antiviral agents and recombinant or subunit vaccines will permit more effective treatment, and possibly prevention, of disease and long-term sequelae associated with EBV infection.