In calling this series Molecular Plant Virology, I had in mind aspects of plant virology of interest to biochemists, molecular geneticists, biophysicists, genetic engineers, or, collectively,molecular biologists. At the same time, the intention was to provide up-to-date reviews, by expert contributors, on current research topics in plant virology of interest and referential use to virologists and plant biologists. The selected topics are pitched mainly at a research level, but with sufficient introduction and cross-referencing to enable graduate students to enter this fascinating field and, hopefully, not get lost.