This manual provides guidance for putting into initial operation a new municipal wastewater treatment plant, a new addition to an existing treatment plant, or a change in the mode of a treatment plant's operation. Information is provided on preparing for actual treatment plant start-up. Preparation for start-up includes: staffing the plant, developing standard operating procedures, conducting dry- and wet-running testing of equipment, providing on-site operator training, conducting safety training, and establishing procedures when construction is continuing during start-up. This manual describes start-up procedures for some of the more common pretreatment and primary treatment units; for the specific secondary treatment processes of activated sludge, trickling filters, stabilization ponds, and aerated lagoons; and for sludge handling units and the anaerobic digestion process. The start-up procedures for advanced wastewater treatment units and processes are not within the scope of this manual. References are provided for additional information on administrative and process considerations; a glossary of pertinent wastewater terms is also included. (Author/BB)