The large, biologically defined, set of arboviruses contains sub-sets representative of a number of different taxons. Arboviruses classified on serological grounds into Groups A and B are now placed respectively into the genera alphavirus and flaviviruses, which form part of the family Togaviridae. The recently defined family Bunyaviridae contains almost 24 different arboviruses, serologically divisible into at least 24 different serogroups. The family Reoviridae includes the genus orbivirus which covers at least 17 serological groups, and the family Rhabdoviridae is another major family which contains a significant number of arboviruses. Outside these four families individual arboviruses are placed in the families Iridoviridae, Poxviridae, Picornaviridae and Coronaviridae, but at least 50 arboviruses remain unclassified.