Anaerobic digestion of animal manure, sewage and other agricultural wastes at psychrophilic temperatures has not been explored as extensively as either mesophilic or thermophilic digestion, probably due to little anticipation of the development of economically attractive systems using this technology. This review article discusses psychrophilic anaerobic digestion studies reported by-various researchers using different substrates. The effect of operational parameters such as type of substrate, size of inoculum, concentration of volatile fatty acids, hydraulic retention time and loading rate, on reduction of TS/VS, BOD/COD and biogas yield is discussed in detail.