Publisher Summary This chapter discusses the importance of soil-contaminant interactions on the risks posed by Hydrophobic Organic Contaminants (HOC) in the soil environment. It is generally accepted that the longer HOCs are in contact with the soil matrix, the lower their potential for transport and availability to ecological receptors. The use of solvent non-extractable residues as an endpoint to judge remediation of contaminated soils has been suggested in the chapter. Microorganisms play a pivotal role in the functioning of the soil ecosystem and their inclusion in the assessment of HOC-contaminated soils is needed. The combination of activity based bioassays with biomarker methods seems to be a promising set of tests to be included in the Ecological Risk Assessment (ERA) process along with tests on higher soil organisms. With natural attenuation and bioremediation of hydrocarbon contaminated sites being increasingly used, ERA needs to incorporate the pivotal role of microorganisms in contaminant degradation.