Papaya ringspot virus (PRSV), a species member of the genus Potyvirus in the family Potyviridae, causes severe damage on cucurbit crops such as squash and melons, and worldwide damage on papaya, a widely grown tropical fruit crop. Leaves of infected plants show mosaic symptoms and are often distorted and shoestring in shape, and infected plants are stunted. Fruit from infected plants can be malformed and show bumps, and infected papaya fruit often show ringspot symptoms, from which the name is derived. PRSV is grouped into type P or type W biotypes based on their host range. The P biotype infects cucurbits and papaya, while the W biotype infects only cucurbits. The virus is transmitted in a non-persistent manner by at least 24 aphid species. Phylogenetic analyzes suggest that PRSV originated in India and spread subsequently to Asia and America. Several viruses closely related biologically and molecularly to PRSV form a common “PRSV cluster”. The worldwide impact of the other viruses is much lower than for PRSV, although they can be locally important or emerging. Control of PRSV consists mostly in prophylactic measures and the use of resistant plants when they are available. Genetically engineered papaya expressing the coat protein gene of PRSV are resistant to the virus and are used commercially in Hawaii, one of only two cases for using commercial transgenic virus-resistant crops in the US.