The book describes fluidized bed gasification of biomass to generate hydrogen rich medium calorific value gas using steam as gasifying medium. Basic studies on steam biomass gasification process have been carried out in a laboratory scale bubbling fluidized bed gasifier and the endothermic heat is supplied by electrical heating. A mathematical model based on thermodynamic equilibrium has been developed to predict the behaviour of thermo-chemical fluidized bed biomass gasification. The subsequent chapters of the work has been devoted to develop a self-sustaining dual fluidized bed gasifier capable of producing medium calorific value gas. The dual bed system has two chambers; bubbling bed gasifier and fast bed combustor. A part of carbon from the gasifier is combusted in the adjoining combustor and the hot bed material from the combustor is circulated back to the gasifier for supplying necessary endothermic heat. The hydrodynamic design of the dual bed system has been carried out through cold model investigation. Based on cold model data, a pilot scale hot dual fluidized bed gasifier has been designed and developed and experiments have been conducted to generate data.