It has been ten years since the publication of the third edition of this seminal text on plant virology, during which there has been an explosion of conceptual and factual advances. The fourth edition updates and revises many details of the previous edition, while retaining the important older results that constitute the field's conceptual foundation. Key features of the fourth edition include: thumbnail sketches of each genera and family groups; genome maps of all genera for which they are known; genetic engineered resistance strategies for virus disease control; latest understanding of virus interactions with plants, including gene silencing; interactions between viruses and insect, fungal, and nematode vectors; and a new plate section containing over 50 full-color illustrations.