Apart from a more economical use of fossil fuels, the application of regenerative energy sources should be advanced in order to reduce CO2 emissions. One of the alternatives Considered to decrease the net emissions of CO2 are the cultivation and combustion of solid biomass, or the thermal utilization of sewage sludge. There are different types of biomass which could be used as energy source in power production: (a) surplus and by-products from agricultural activities within the European Union (EU), e.g., straw, (b) fast growing energy plants from reutilization of areas which become available by a necessary reduction of agricultural overproduction within Europe, and (c) wood waste from forestry or wood processing. In order to achieve a noticeable CO2 reduction, as well as fossil fuel substitution, it is desirable to use fairly large quantities of biomass for energy production. However, an exclusive biomass utilization would consequently lead to the construction of many decentralized plants, which is time-consuming and would require high financial investments as well as large storage capacities due to the seasonal fuel availability. Go-combustion, in contrast, is considered to be a cheap option for utilizing the existing biomass resources. For these reasons, an EU-project, ＇Combined Combustion of Biomass/Sewage Sludge and Coals of High and Low Rank in Different Systems of Semi-industrial and Industrial Scale＇ was launched in 1993. Under the coordinatorship of the Institut fur Verfahrenstechnik und Dampfkesselwesen (IVD), University of Stuttgart, partners from eight European countries investigated the effects of burning sewage sludge, agricultural residuals, such as straw and manure, as well as especially cultivated energy plants in combination with coals of various ranks and origin. Both the pulverized fuel (PF) and the fluidized bed (FB) mode were tested, ranging from laboratory rigs to large scale utility boilers. This paper provides an overview of the activities of the various partners involved and will, in particular, show the synergetic cooperation towards a common aim. The results of the 2-yr project will be summarized.