The genetics of resistance to disease is an area of great interest in agriculturally important plant and animal species. Selective breeding for resistance to pathogens in plants, animals and insects has demonstrated that resistance and susceptibility to pathogens are controlled by both genetic and environmental factors. The immune loci causally involved in susceptibility and resistance to disease are currently unknown. However, novel enabling molecular technologies promise to assist in unravelling the genetics of the host response to infectious diseases in new ways, and ultimately to improve seed stock genetics.