Growing in their natural environments, the majority of plants remain healthy.There may be some flecking or leaf distortions, but most plants competeeffectively and produce the next generation. This relative vigour is becauseplants have evolved an effective immune system that protects each of theircells from the majority of pathogens and pests. Only parasitic strains thathave developed mechanisms to overcome multiple layers of plant innateimmunity are able to invade and cause disease. Once disease takes hold itcan be devastating, particularly in plant monocultures that have a narrowgenetic base. The predicted increase in numbers of human beings having tosurvive on our planet, as areas of fertile soil to grow crops become more scarceand production costs soar, brings into sharp focus the need to understandbetter molecular processes of plant disease and plant disease resistance. Themajority of the world’s populations still battle against malnutrition, hostileenvironments and crop infestations. A heavy reliance on pesticides both inWestern agricultural systems and in the developing world helps to maintaincrop yields but is environmentally damaging and costly. The impetus hastherefore never been stronger to comprehend better how pathogens evolve toinfect particular plant species, how certain plant genotypes naturally defendthemselves against pathogen infection and how plant disease resistance isexecuted at the level of individual cells, whole organisms and ecosystems.