Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Wherever life is found, so are viruses. The hot and acidic waters of hot springs, such as those in Yellowstone National Park, are no exception. Species of the archaeal organism Sulfolobus thrive at high temperatures and low pH and are host to a number of virus strains, including the double-stranded DNA virus Sulfolobus turreted icosahedral virus (STIV). The characterization of STIV particles and virus-encoded proteins is leading to a better understanding of the origin and evolution of this group of viruses. (See related article in August 2006: vol. 80, issue 15, page 7625.)