Stanley Ben Prusiner (1942- present) was awarded the 1997 Nobel Prize in Physiology or Medicine for his discovery of the disease-causing proteins called prions. While studying a little-known class of neurodegenerative disorders called spongiform encephalopathies, Prusiner isolated what he believed to be its agent, the prion. He concluded that the prion was unlike any other known pathogen because it was comprised of only protein, lacking a means of replication. Initially met with criticism, Prusiner’s prion theory was accepted in the mid-1990s, and became relevant when an encephalopathy called variant Creutzfeldt-Jakob disease emerged. Prions may also help us to understand disorders such as Alzheimer's disease and Parkinson's disease, which share certain characteristics with diseases caused by prions.