Technical Abstract: Genetic resistance to root diseases of plants is rare, and agriculture controls these diseases by practices such as crop rotation and soil fumigation. However, plants have evolved a strategy of stimulating and supporting specific groups of antagonistic rhizosphere microorganisms as a defense against diseases caused by soilborne pathogens. Antibiotic production plays a significant role in plant defense by many of these bacteria, and detailed information is now available about the genetics, biochemistry, and regulation of synthesis of several commonly-produced antibiotics. Similarly, many genes that contribute to the ability of these strains to colonize roots have been identified, and studies of naturally suppressive soils have provided evidence of preferential interactions between plant hosts and biocontrol bacteria, revealing the existence of functional diversity in protective populations of very closely related strains. Here, we consider how this knowledge can be applied to better manage the indigenous rhizosphere microflora, aid in the selection of more effective microbial amendments, and guide the tailoring of microflora through directed genetic manipulation to enhance crop health and productivity.