A variety of techniques have been used to examine plant viral genomes, the functions of virus-encoded proteins, plant responses induced by virus infection and plant-virus interactions. This overview considers these technologies and how they have been used to identify novel viral and plant proteins or genes involved in disease and resistance responses, as well as defense signaling. These approaches include analysis of spatial and temporal responses by plants to infection, and techniques that allow the expression of viral genes transiently or transgenically in planta, the expression of plant and foreign genes from virus vectors, the silencing of plants genes, imaging of live, infected cells, and the detection of interactions between viral proteins and plant gene products, both in planta and in various in vitro or in vivo systems. These methods and some of the discoveries made using these approaches are discussed.