The Potyviridae represent 30 percent of all plant viruses and are economically the most important group, causing diseases on a wide range of temperate and tropical crops. The last decade has witnessed major advances in our knowledge of their molecular structure, genome organization, mode of replication and polyprotein processing and variation. In this book these new molecular insights are collated and presented in the context of accumulated information on the biology and symptomatology of this family of viruses. Including a comprehensive literature review, the volume is an essential reference for virologists and plant pathologists.