Methods used for modelling submicronic wet grinding processes are discussed. Simplified solutions of the population balance equation are first tested on experimental results obtained during batch runs performed with media mills on different materials. The use of statistical laws for modelling multimodal particle size distributions resulting from size reduction and aggregation processes is then presented. Finally, a method of macroscopic modelling to predict the particle size distribution of product from continuous ultrafine grinding is presented. It combines batch grinding kinetics and a solids flow model. (C) 2004 Elsevier B.V. All rights reserved.