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depend on the ability to accurately predict the fundamental properties of the system, specifically, the hydrodynamics, the mixing of individual phases, and the heat and mass transfer properties. Identification of the flow regimes under which the system operates is crucial to an understanding of both the variations of these properties and overall system performance. This timely, comprehensive review describes in a systematic manner the status of fundamental gas-liquid-solid fluidization behavior. This review also discusses the areas in which current knowledge is deficient and further research is needed. SCOPEGas-liquid-solid fluidization is defined as an operation in which a bed of solid particles is suspended in gas and liquid media due to the net drag force of the gas and/or liquid flowing opposite to the net gravitational force or buoyancy force on the particles. Such an operation generates considerable, intimate contact among the gas, liquid and solid particles in these systems and provides substantial advantages for applications in physical, chemical or biochemical processing involving gas, liquid and solid phases.Various modes are possible for gas-liquid-solid fluidized-bed operation. The gas-liquid-solid fluidized bed can be operated with a cocurrent or countercurrent flow of a gas and a liquid with gas as the continuous phase. It can also be operated with a cocurrent or countercurrent flow of a gas and a liquid with liquid as the continuous phase. The states of fluidization are altered when the fluidized bed is tapered, or an upper retaining grid or a draft tube is present in the bed.This review examines both the experimental and modeling studies of the fundamental characteristics of gas-liquid-solid fluidization. Specifically, a comprehensive review is made on the hydrodynamics, the mixing of individual phases, and the heat and mass transfer behavior of various modes and states of gas-liquid-solid fluidization. Industrial application of the gasliquid-solid fluidized bed is briefly described. CONCLUSIONS AND SIGNIFICANCEGas-liquid-solid fluidization became a subject for fundamental research only about two decades ago. Considerable progress has been made with respect to an understanding of the phenomena of gas-liquid-solid fluidization since then. This review summarizes and analyzes the available information in the literature on this subject.Gas-liquid-solid fluidization can be classified mainly into four modes of operation. These modes are: cocurrent three-phase fluidization with liquid as the continuous phase (Mode 1-a); cocurrent three-phase fluidization with gas as the continuous phase (Mode 1-b); Inverse three-phase fluidization (Mode IJ-a); and fluidization represented by a turbulent contact absorber (TCA) (Mode II-b). Modes II-a and 11-b are achieved with a countercurrent flow of gas and liquid. Due to the complex nature of three-phase fluidization, however, various methods are K Muroyama is on leave from the Department of Environmental Chemistry and Technology, Tottori University, Tottori, 680, Japa...