The materials issues in fluidized bed combustion systems are in many cases essentially similar to those in conventional pulverized coal systems. Those that are related to the technology itself include the erosion and corrosion of in-bed components, particularly the heat exchanger; the erosion of above-bed components; the wear (perhaps accelerated by corrosion) of the solids handling systems, particularly the ash recirculation system; and, in the case of pressurized combustors, the erosion and hot corrosion of the expander turbine. For steam-generating systems, the issue of in-bed corrosion is probably not as serious as had once appeared, provided care is taken in materials selection, in design, and in operation. In-bed erosion now appears to be the most important problem to be solved. The expander turbine problems define the degree of particulate removal from the hot gas that has to be achieved, and limit the maximum permissible bed temperature. However, both the erosion and corrosion may be easier to deal with in the low-temperature expander in the “pressurized boiler” concept.