A review which provides an essential understanding of the fluidization theory, a system description of the fluid-bed processor, and a description of the critical variables associated with equipment, product and process.Upon gaining this basic understanding, one can design scale-up protocols.How critically process variables are identified at an early stage of the product development and then extrapolated based on the knowledge of the equipment variables and tolerances, and material handling considerations, will provide a trouble-free batch size increase.