The disposal of solid waste has become an increasingly difficult and costly problem. Environmental regulations have restricted incineration and ocean dumping, and costs for landfilling have escalated. The calorific value of municipal solid waste (MSW) is about 12.5 MJ/kg on a dry basis (9.8 MJ/kg as received). Therefore, conversion of MSW to marketable fuels has become a noble goal from both an ecological and an environmental standpoint. Typically MSW consists of approximately 60% combustible organics such as paper, newsprint, packing material, wood wastes, yard clippings, food wastes, plastics, and textiles. The remainder is comprised of moisture, glass, metals, and other inorganic wastes. The composition of MSW varies from place to place and on a daily basis. Therefore, there is a need for a method to rapidly characterize these wastes. This communication shows that thermogravimetry (TG) can be used to obtain information on the moisture, cellulosics, plastics, fixed carbon, and ash content of solid wastes and refuse derived fuels (RDF). This procedure is of importance since no ASTM procedures are available to determine the compositions of cellulosic, plastic, and biomass materials. The weakness of the classical ASTM method for proximate analysis of coals and its usage in the biomass area are highlighted. When compared to the classical ASTM method, TG provides additional information on the kinetics and reactivity of materials. Methods for utilizing TG data to obtain information on the composition and reactivity of solid materials are discussed. Broido and Coats-Redfern type equations provide unique Arrhenius parameters.