An overview is given of modem air classification devices, their operation principles, features and parameters, as cut size, cleanness and recovery. We outline the separation zones common to existing classifiers. In practice, various gravitational and centrifugal classifiers are employed, including those with vertical and horizontal air streams, cascade classifiers, fluidized bed separators, inertial, vortex, rotor classifiers, etc. Choice of the classifier type and designs is dictated by the technological requirements (throughput, cleanness, etc.) and the properties of materials to be classified. Advantages and limitations of the classifiers and basic trends in their development are considered. (C) 2004 Elsevier B.V. All rights reserved.