Studies by the Rand Corporation in the 1980s identified substantial differences in the scale-up and start-up performance of plants processing particles versus those processing liquids or gases. These differences were inevitably unfavorable. Particulate process plants take longer to start up and are less likely to achieve desired production rates. Facility operators often underestimate the challenges involved. These problems generally relate to an inadequate understanding of the behavior of particle systems. Many of these behaviors are sensitive to process scale or process history in ways that would not be expected by engineers familiar only with liquid or gas systems. Empiricism must often substitute for first principles. Modeling provides some answers, but often not enough to eliminate the need to operate pilot plants. This paper reviews some of the unit operations involved in particle processing and highlights scale-up issues involved. The use of information from suppliers and other third parties is discussed, as well as scale-up strategies in competitive or regulated industries. (c) 2004 Elsevier B.V. All rights reserved.