Mixing of powders and granular materials of different functions and/or properties is frequently encountered by engineers and scientists. Nevertheless, the guidelines for the selections of particle mixers are still not fully developed and predictions of the mixture quality after mixing operations are still not possible. These are largely due to the fact that the tools for particle mixing studies are far from well developed. In the last decades, advances in experimental and computational methods have brought lights to better particle mixer design and operation. This paper reviews the tools for the investigation of mixing in particulate systems. (c) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.