Obligately anaerobic fungi are part of the natural microflora of the alimentary tract of many herbivorous mammals. They produce a complete set of polysaccharide hydrolytic enzymes which efficiently degrade plant cell-walls. This article summarizes the present work on biomass degrading enzymes with special emphasis on their cellulases, xylanases, and esterases from both monocentric and polycentric anaerobic fungi. The possibility of the cellulosome or xylanosome-like high molecular mass complexes in the fungi are also discussed.