The production of proteins in large quantities can easily be accommodated by plants, which present a rich source of biomass. Specifically, the use of  plant viral expression vectors to express foreign proteins by transient expression has several advantages over constitutive expression in transgenic plants. For example, plant virus-based expression vectors can be used to express proteins which are potentially toxic and cannot be expressed in transgenic plants. In general, plant viruses can express higher levels of foreign protein. Furthermore, many of the biosafety concerns surrounding transgenic plants can be avoided using plant virus-based expression. In the past, expression of the foreign protein as a fusion to a viral protein or from a duplicated subgenomic mRNA promoter has been the focus of most approaches for the expression of foreign genes. In this chapter, the most recent strategies that have been developed to utilize plant virus-based expression systems for a multitude of purposes are examined. The ‘deconstructed virus strategy’ versus the ‘full virus strategy’ of plant virus-based expression vectors is covered in the chapter. Various means by which conventional plant virus vectors can be improved and their application for both commercial use and as a research tool are discussed.