Stack emissions from three municipal refuse-to-energy systems were characterized: refuse-derived fuel (RDF), mass burning (MASS) and modular (MOD). A comprehensive set of measurements was performed at each site to determine the physical and chemical properties of the particulate and gaseous stack emissions. The physical characterization included measurement of the mass concentration, and size distribution of the stack particulate matter. Inorganic chemical characterization of the stack emissions included determination of the elements, anions, and compounds present in the fly ash, measurement of gaseous HCl and HF emissions, and determination of volatile trace element levels. The characterization of organic materials in the stack emissions included specific measurements for polynuclear aromatic hydrocarbons (PAH), tetrachlorinated dibenzo-p-dioxins (TCDD) and dibenzofurans (TCDF), and aldehydes. Screening analyses were performed to provide tentative identification of organic compounds in the stack emissions.