David M. Weller discusses the use of bacteria for biological control of soilborne plant pathogens in the rhizosphere. Biological control has been studied for over 65 years, but was not considered commercially feasible until the 1960s. Recent advances in understanding the rhizosphere and selecting strains adapted to it have led to successful field applications. Bacteria such as Agrobacterium radiobacter strain 84, Bacillus subtilis A13, and Pseudomonas fluorescens 2-79 have shown effectiveness in controlling various plant pathogens. These bacteria improve plant growth by suppressing pathogens and possibly stimulating plant growth. The effectiveness of bacterial biocontrol agents depends on their ability to colonize roots and compete with pathogens. Factors such as soil conditions, root colonization patterns, and bacterial traits like surface polysaccharides, fimbriae, flagella, chemotaxis, osmotolerance, and complex carbohydrate utilization influence their success. Siderophores, antibiotics, and induced resistance are mechanisms by which bacteria suppress pathogens. However, inconsistent performance is often due to factors such as loss of ecological competence, presence of non-target pathogens, and variable root colonization. To improve the effectiveness of bacterial biocontrol agents, research is needed to understand the interactions between bacteria, pathogens, and the environment. This includes developing better formulations, improving root colonization, and understanding the mechanisms of pathogen suppression. Future research should focus on enhancing the consistency and effectiveness of bacterial biocontrol agents for commercial use.David M. Weller discusses the use of bacteria for biological control of soilborne plant pathogens in the rhizosphere. Biological control has been studied for over 65 years, but was not considered commercially feasible until the 1960s. Recent advances in understanding the rhizosphere and selecting strains adapted to it have led to successful field applications. Bacteria such as Agrobacterium radiobacter strain 84, Bacillus subtilis A13, and Pseudomonas fluorescens 2-79 have shown effectiveness in controlling various plant pathogens. These bacteria improve plant growth by suppressing pathogens and possibly stimulating plant growth. The effectiveness of bacterial biocontrol agents depends on their ability to colonize roots and compete with pathogens. Factors such as soil conditions, root colonization patterns, and bacterial traits like surface polysaccharides, fimbriae, flagella, chemotaxis, osmotolerance, and complex carbohydrate utilization influence their success. Siderophores, antibiotics, and induced resistance are mechanisms by which bacteria suppress pathogens. However, inconsistent performance is often due to factors such as loss of ecological competence, presence of non-target pathogens, and variable root colonization. To improve the effectiveness of bacterial biocontrol agents, research is needed to understand the interactions between bacteria, pathogens, and the environment. This includes developing better formulations, improving root colonization, and understanding the mechanisms of pathogen suppression. Future research should focus on enhancing the consistency and effectiveness of bacterial biocontrol agents for commercial use.