From a technological standpoint, numerous operations in chemical and processing industries involve fluid-particle systems. Fluidization technology relies almost solely on fluid-particle (solid and bubbles) interactions. Hydraulic and pneumatic transportation of particulate materials involves hydrodynamic interactions between the conveying medium (liquid/gas) and the material to be transported. Other examples of solid-fluid interactions include the filtration of polymer melts, sewage sludges and paper coatings, sedimentation and thickening of slurries, disposal of wastes from mineral industries, interpretation of the rheological behavior of suspensions, trickle bed, fixed bed, and slurry rectors, etc. Less appreciated applications of fluid-particle systems include the motion of red blood cells in capillary flow, chromatographic separations, electrophoresis, separation of macromolecules according to their sizes, etc. The most common method to affect gas/liquid contacting is to introduce the gas through a multihole distributor in the form of tiny gas bubbles. Naturally, the rates of transfer processes and chemical reactions are essentially governed by the flow field established around the ascending gas bubbles. Introduction of an inert gas into a pool of liquid to improve mixing is a commonly used process in metallurgical and chemical industries. Dispersion of a liquid in another immiscible liquid, resulting in an emulsion, is indeed a basis for the manufacture of a class of polymers, cosmetics, personal care products, toiletries, foodstuffs, metallic foams, and alcoholic beverages, etc. Thus there is no dearth of examples of industrial relevance involving interactions between bubbles, drops, and particles and a flowing or stagnant continuous fluid phase.