Hans Ris (1914-2004) was an American cytologist and pioneer electron microscopist. His studies of chromosome structure revealed the importance of non-histone proteins and he was one of the first to recognize that blue-green algae was a special type of bacteria. He coined the term genophore for prokaryote DNA. Elected to the National Academy of Sciences in 1974, he was a founder of the American Society for Cell Biology. The Hans Ris papers consist of correspondence, research notes, published and unpublished works by Ris and others, related to the latter part of his career. The bulk of the collection contains micrographs from the High Voltage Electron Microscopy (HVEM).