The desire and need to reduce energy requirements is, of course, the first and foremost reason for seeking a better understanding of the role of classification in closed circuit coal grinding. A better understanding of classifiers typically used in conjunction with coal grinding circuits would result in the ability to better utilize energies expended in coal grinding. In addition, the ability to better control the product size distribution is of major importance to many new processes being introduced to our energy conscious economy. Such processes include coal-oil mixture production, the production of coal-water slurries of pipelines, coal gasification and the production of solvent refined coal. All of these processes call for the use of pumpable and high concentrate slurries. In all cases the particle size distribution has a direct effect on the pumpability and percent by weight solids concentration that is reasonably attainable. Recognizing the need for a better technical understanding of classifiers used in coal grinding, the United States Department of Energy and the Kennedy Van Saun Corporation conceived the present project to evaluate various classifiers currently being used in air swept coal grinding systems. The classifiers under consideration include a twin cone classifier, an expansion chamber type (vari-mesh) classifier and a new centrifugal classifier recently introduced by Hukki. The objectives of this evaluation are to compare the classifiers with respect to their effect on closed circuit grinding system performance and to provide data that will allow a preliminary evaluation of classifier design with respect to separation on the basis of sulfur and ash content.