This article discusses the virology of Epstein-Barr virus (EBV) and provides an overview of the disease states associated with the virus, describes how the immunology of EBV infection provides for control in the normal host, and reviews what is currently known about post-transplant lymphoproliferative disorder (PTLD), including evidence for EBV in the pathogenesis of PTLD, risk factors for its development, clinical presentation, methods for diagnosis, pathology, treatment, and current and future preventive strategies.