Most estimates of the total loss of worldwide agricultural production to pests, pathogens and weeds suggest figures of between 20 and 40 percent. A major goal therefore in current plant biotechnology is the modification of plant genomes to produce crops with enhanced resistance to pests, pathogens and herbicides. This will permit crop protection with reduced levels of application of chemical insecticides and fungicides, and the more selective use of herbicides. This book reviews our current knowledge of this rapidly advancing field and will be of great interest to plant biotechnologists and genetic engineers, as well as workers in plant pathology or agricultural entomology wishing to keep abreast of the subject.