This CEN report compiles the experience collected from the co-combustion of biomass and waste by 2002. The data and the test results are given from systematic research projects and from investigations on fly ash obtained from co-combustion in different power plants in the framework of national certification processes or from other co-combustion tests. The report: - includes the existing national regulations for the demonstration of the suitability of fly ash from co-combustion, - gives a survey on the combustion materials used so far, - describes the chemical composition of fly ashes obtained from co-combustion, - lists the chemical and physical properties of the fly ashes, which are relevant to the technical and environmental properties of concrete, - includes test results of properties of concrete with fly ashes obtained from co-combustion.