Diseases induced by soil-borne plant pathogens are among the most difficult to control. Prophylactic methods aiming at preventing the introduction of pathogens in healthy soils have to be respected, because it is almost impossible to eradicate pathogens from an infested field soil. Even the drastic disinfestation techniques based on the application of biocide molecules such as methylbromide failed to eliminate the pathogens, but are harmful to man and the environment. Growers should prefer new, environment friendly techniques such as solarization and biological disinfestation of soils. These methods induce changes in the microbial balance, reducing the population density of the pathogens and stimulating the activity of some beneficial microorganisms. The study of soils that naturally suppress diseases induced by soil-borne pathogens has led to a better understanding of the interactions between pathogenic and antagonistic microorganisms and has resulted in the selection of biocontrol agents.