Contaminants entering the soil environment as by-products of industrial or technological processes undergo various transformations. Some easily undergo degradation, volatilization or leaching, some are accumulated in the living organisms, while others get strongly bound to soil components through sorption, sequestration or bound-residue formation. In literature, it has been proved that the above mentioned processes considerably limit the bioavailability of contaminants and hence the effectiveness of biodegradation is lowered. The present study is a review of the literature on the issue of bioavailability of persistent organic pollutants for microorganisms and soil invertebrates. The first part presents some definitions of bioavailability and bioaccumulation proposed by various authors. Factors influencing the process of biodegradation have also been described with special attention drawn to their relation to the processes of bioavailability.