Most central nervous system diseases that lead to severe neurologic dysfunction or death are caused by viruses and abnormally configured proteins called prions. This new issue of Neuroimaging Clinics, Guest Edited by Turgut Tali, explores the imaging used to detect these diseases. Articles cover topics on Neuropathology of Virus Infections of the CNS, Imaging of "slow viruses" Infections of the CNS, Imaging of Post-infectious Encephalomyelitis, and Imaging of HSV Infections of the CNS.