Enteric viruses of poultry are common and pervasive. They are potentially as diverse as enteric bacteria and are responsible for production diseases resulting in substantial financial losses. Many of these viruses have RNA genomes that continually evolve, leading to multiple circulating strains of varying pathogenicity. They can be difficult to diagnose due to confounding issues, such as their presence in healthy birds, variable pathogenicity, age-related resistance, coinfection with other pathogens, and lack of convenient diagnostic tests. They are associated with complex syndromes, such as malabsorption syndrome of broiler chickens and poult enteritis mortality syndrome, but also of diseases outside the enteric system, such as tenosynovitis caused by avian orthoreovirus. Recent metagenomics studies are beginning to shed light on the causes of some complex production diseases, and some of the more prominent virus families are described in this chapter, including astroviruses, coronaviruses, parvoviruses, picornaviruses and rotaviruses.