Tremendous progress in the availability of genomic data has been made in the past decade. With the advent of high throughput and affordable DNA sequencing, the entire hereditary blueprint of an organism can be determined. A widespread transition into research enabled by the tools and resources of genomics is consequently occurring, and it has already affected countless disci-plines within the biological sciences, in-cluding plant pathology. This new era of research allows a comprehensive study of gene structure and function and has al-ready delivered tremendous insights into the basic biology of living organisms. Ge-nomics offers new opportunities for ap-plied biological sciences and is poised to impact plant health and plant disease man-agement. More than 150 years have elapsed since Phytophthora infestans caused the Irish potato famine, but strategies for managing potato and tomato late blight often remain unsustainable and costly. In effect, P. in-festans continues to cost billions of dollars annually through losses in potato and to-mato production and increased fungicide costs (15,45,47,48). In the United States and other developed countries, chronic use of chemicals to manage late blight reduces the profit margins of farmers and is not always successful. Most populations of the pathogen are resistant to metalaxyl (and the active enantiomer mefenoxam), which had previously been very successful for controlling P. infestans (19,47). In devel-oping countries, late blight also affects subsistence potato production. Recent epidemics in the 1990s, notably in eastern Europe, have caused significant losses in yield (20,46). In 2003, potato production was nearly eliminated in Papua New Guinea, one of the few countries in the world that was previously free of the dis-ease (4). Remarkably, the disease spread through the entire country within 2 months of first incidence. Disturbing reports pre-dict that potato late blight will continue to cause food shortages and hunger in several parts of the world (20,46). Fig. 1. Schematic view of infection cycle of Phytophthora infestans on A, susceptible, and B and C, resistant plants. A, (i) zoospore, (ii) cyst, (iii) germinating cyst, (iv) germi-nated cyst with appressorium, (v) germinated cyst with appressorium and infection vesicle, (vi) haustorium, (vii) sporangium. B and C, Similar to panel A except that plant cells undergoing hypersensitive cell death are shown in red. The hypersensitive re-sponse can include groups of plant cells (B) or 1 to 2 cells (C) depending on the geno-types of plant and pathogen. Plant Disease / July 2005 693 The study of late blight has entered the genomics era (11,33,44). Genome se-quencing and the development of genom-ics-enabled technologies is proceeding not only for P. infestans but also for its pri-mary host plants, tomato and potato (26). Although the technology of genomics is in its infancy, we are already experiencing the potential that it offers in understanding plant disease and improving plant health. The objective of this article is to illustrate the applications that genomics offer for managing potato and tomato late blight and to review how genomics has improved our understanding of P. infestans pathology.