Technical Abstract: Suppressive soils have been described worldwide for a broad spectrum of plant pathogenic fungi, bacteria and nematodes. Classical approaches employed to identify the microorganisms and mechanisms involved in suppression have changed little during the last four decades. However, when classical approaches are used in combination with sophisticated techniques of molecular ecology, it is possible to more rapidly define and characterize the agents and mechanisms responsible for specific suppression. Mechanisms of suppressiveness operating in several suppressive soils are discussed below.