Development of fluidized bed fire-tube and water-tube boilers for the burning of wood, gas, and refuge-derived fuel will be reviewed. Experience gained in already installed plants will be outlined. Research experiments results on the use of various forms of wood and other biomass fuels, such as wood chips, pellets, peach pits, nut shells and kernels, and refuse-derived fuels, will be described for small and medium sized fire-tube boilers, and for larger water-tube boilers for co-generation.