Plant diseases have major effects on agricultural production and the food supply. Currently, worldwide crop losses due to disease are estimated to exceed hundreds billion dollars. Although application of fungicides and pesticides has helped control plant diseases, chemical control is economically costly as well as environmentally undesirable. Therefore, the development of new strategies based on a plant’s own defense mechanisms for disease control is critical for sustaining agricultural production and improving our environment and health. From this point of view this review how plant immune system work against pathogen?