Plant immunity is the inherent or induced capacity of plants to withstand or ward off biological attack by pathogens, biotic and abiotic stress. Molecules released from pathogens are recognized by plant cell surface receptors, and trigger specific signaling cascades that help to defend the plant against attack. As pathogen evolution can overcome disease resistance that is conferred by individual plant resistance genes, an enhanced understanding of the plant immune system is necessary for the long-term development of effective disease management strategies. The plant immune response culminates in the production of a myriad of antimicrobial agents including reactive oxygen species, secondary metabolites, hydrolytic enzymes, and antimicrobial peptides and proteins. Increasing the accumulation of antimicrobial compounds of different biological origin (plant or microbial) in transgenic plants represents a promising strategy for engineering plant disease resistance against fungal and bacterial pathogens.