Presented is a review of recent advances in the chemistry of abiotic redox transformations of organic pollutants in anaerobic ecosystems. Particular attention is given to the types of functional groups that undergo reaction and the findings concerning physical and chemical parameters of ecosystems that govern the rates and products of redox transformations. Classes of compounds and structural features within these classes of compounds provide information about the intrinsic nature of the natural reductants. Further information is provided by studies that consider system variables such as sediment concentrations, organic carbon levels, pH, Eh, and temperature. While the identity of reducing agents that transform organic pollutants in anaerobic systems remains elusive, the reactivities of these agents are being characterized and compared with surrogate (model) reductants. It is apparent that chemical and biological reduction processes are strongly coupled, and there is increasing evidence for widespread mediation of reductive reactions by bio-organic molecules.