Pasteurization of municipal wastewater sludge is of interest in Europe and North America to meet regulations for certain uses of the material. For technical reasons, pasteurizing the sludge prior to mesophilic anaerobic digestion is preferred. This paper discusses the various methods currently employed to meet the temperature/time requirements of pre-pasteurization. Batch and continuous flow pre-pasteurization reactors are discussed with evaluation of how mixed or semi-mixed pasteurization tanks could provide pathogen control required for disinfected or Class A sludge (biosolids), as defined by the U.S. EPA. Key issues with respect to pre-pasteurization systems are discussed, based on recent experience.