Borna disease virus is an agent distinct from all known viruses. Pathogenesis of its infection is also unique. This review highlights several aspects of the biology of this viral infection and the preliminary characterization of the agent. BDV can be used to answer important questions in neurobiology. These include neuroinvasiveness and neurotropism of viral agents, CD4+ T cell-mediated immunopathology and tolerance in newborn animals to a persistent viral infection in the CNS and behavioral diseases and eating disorders induced by neurotropic viruses. This review is dedicated to Prof. Dr. Rott on occasion of his 65th birthday in recognition of his immense contributions to studies on Borna disease and also for his success focusing the attention of the scientific community to this still evolving unique viral disease.