Soils represent a major sink for organic xenobiotic contaminants in the environment. The degree to which organic chemicals are retained within the soil is controlled by soil properties, such as organic matter, and the physico-chemical properties of the contaminant. Chemicals which display hydrophobic and lipophilic characteristics, as well as a recalcitrant chemical structure, will be retained within the soil, and depending on the `strength' of the association may persist for long periods of time. This review describes the behaviour of hydrophobic organic contaminants in soils, focusing on the mechanisms controlling interactions between soil and contaminants. The bioavailability of contaminants in soil is also discussed, particularly in relation to contact time with the soil. It considers the degradation of organic contaminants in soil and the mechanisms microbes use to access contaminants. Finally, the review discusses the `pros' and `cons' of chemical and biological techniques available for assessing bioavailability of hydrophobic organic chemicals in soils, highlighting the need to quantify bioavailability by chemical techniques. It concludes by highlighting the need for understanding the interactions between the soil, contaminants and biota which is crucial to understanding the bioavailability of contaminants in soils.