Cucumber mosaic virus (CMV) has a worldwide distribution and a remarkably broad host range of over 1000 plant species, including many agronomically important horticultural crops. The virus is transmitted horizontally by over 80 species of aphids in a non-persistent manner, as well as vertically, through the seed, in certain host species. The CMV genome consists of three, single-stranded, positive-sense RNAs encapsidated separately in isometric particles of 29 nm in diameter. The CMV genome encodes five proteins expressed from either the three genomic RNAs or two sub-genomic RNAs. Control strategies include sanitary selection, prophylactic measures and use of resistant plant cultivars.