The presentation reviews current developments in sludge digestion that have been applied on a full scale in the United States and predicts future developments. Full scale experiments using thermophilic digestion at Los Angeles and at Chicago are described. Results of the evaluation of dual digestion (oxygen aerobic digestion followed by anaerobic digestion) at Hagerstown, Md., are presented. New developments, such as multiple digestion, developed by W. Torpey, are discussed. The impact of federal programs that encourage conservation of energy has greatly increased use of the excess methane produced in anaerobic digestion of sludge. Implications of the dependence created on this internally generated energy are presented. Research areas of high potential are also addressed.