Multiphase reactors are found in diverse applications such as in manufacture of petroleum-based fuels and products, in production of commodity and specialty chemicals, pharmaceuticals, herbicides and pesticides, in refining of ores, in production of polymers and other materials, and in pollution abatement. In all such applications, the knowledge of fluid dynamic and transport parameters is necessary for development of appropriate reactor models and scale-up rules. The state of the art of our understanding of the phenomena occurring in three-phase reactors such as packed beds with two-phase how, slurry bubble columns and ebullated beds is summarized in this review.