Encephalitis is an acute inflammation of the brain that is caused by a viral infection. Several viruses, herpes simplex virus type 1 (HSV-1), Varicella zoster virus (VZV), cytomegalovirus (CMV), West Nile virus, and certain members of the Flavivirus family or Bunyavirus genus for example, can cause encephalitis. Although these viruses have very different biological properties, they have the ability to enter the central nervous system, replicated in neurons, and can all cause encephalitis. In general, patients with encephalitis suffer from fever, headache, seizures, and photophobia. Less commonly, stiffness of the neck can occur with rare cases of patients also suffering from stiffness of the limbs, slowness in movement and clumsiness depending on which part of the brain is involved. Encephalitis is not a typical outcome of viral infections, but it is life threatening and difficult to treat. This chapter discusses the properties of the viruses that cause encephalitis, how they cause clinical disease, and the available therapeutic strategies that are available. [ABSTRACT FROM AUTHOR]