Rotaviruses are significant enteric pathogens of humans and animals. Rotavirus-associated mortality is still high in children, especially in developing countries. Rotaviruses also account for important economic losses due to gastrointestinal disease of livestock animals, notably of young cattle and pigs. Increasing numbers of different rotavirus strains stress the necessity of their uniform nomenclature and detailed classification with the use of whole-genome sequencing. Phylogenetic analyses of the rotavirus genome reveal repeated intersections between the evolution of human and animal rotavirus strains which is probably a consequence of multiple events of transmission among various animal species. The interspecies transmission and subsequent gene reassortment are important mechanisms driving the diversity of rotaviruses and enabling the emergence of new pathogenic strains.