Aphids are the most common vector of plant viruses. Mechanisms of transmission are best understood by considering the routes of virus movement in the aphid (circulative versus non-circulative) and the sites of retention or target tissues (e.g. stylets, salivary glands). Capsid proteins are a primary, but not necessarily sole, viral determinant of transmission. A summary is presented of the taxonomic affiliations of the aphid transmitted viruses, including 8 families, 18 genera, and taxonomically unassigned viruses.