Viruses infecting members of Archaea, the third domain of life, constitute an integral, yet unique part of the virosphere. Many of these viruses, specifically the species that infect hyperthermophilic hosts, display morphotypes – for example, bottle shaped, spindle shaped, droplet shaped, coil shaped, bacilliform – not known to be associated with the other two cellular domains, Bacteria and Eukarya. The distinctiveness of the hyperthermophilic archaeal viruses extends to their genome sequences: a large majority of the predicted genes yield no sequence matches in public databases and encode proteins with exceptional structures and unknown functions. Moreover, the ways in which these viruses interact with their hosts are also unique, as indicated by a unique virion egress mechanism, which involves formation of pyramidal portals on the cell surface. Some viruses that infect extremely halophilic Archaea are morphologically highly similar to head‐tail bacterial viruses of the order Caudovirales and apparently share an ancestry with them. Identified archaeal viruses almost exclusively carry double‐stranded deoxyribonucleic acid (DNA) genomes and only a few species have single‐stranded DNA genomes.