Transgenic tobacco expressing the cucumber mosaic virus coat protein has been reported to be highly resistant under natural field conditions. This chapter focuses on several different molecular strategies that have been developed or proposed for the control of plant-virus diseases. Broad-spectrum resistance to several different viral groups may also be obtained through a multiple integration process. C. Lawson et al. used a double coat protein transformation vector to obtain multivirus resistance in transgenic potato expressing both potato virus X and potato virus Y coat proteins. There are a number of different strategies for using molecular technology to integrate or create new resistance factors in plant-virus systems. In general, coat protein-mediated resistance is correlated with a delay in symptom development and is dependent upon the concentration of challenge inoculum. Coat protein-mediated resistance in many systems is generally limited to protection against the homologous virus or virus strains closely related to the integrated coat protein gene.