The object of this paper is to discuss various ball mill classifier arrangements, which can be used in wet-grinding practice. Almost every metallurgist, directing a modern milling plant, has to determine the most efficient way to reduce the mill feed to some predetermined mesh by means of the wet grinding process. The following comments on various combinations of ball mills and classifiers are based on general theoretical considerations and on data taken when operating many of the circuits described. Any discussion of the conditions under which the various circuits described operate at highest efficiency, is outside the scope of this paper.