The design and modelling of crystallisation processes without recourse to experimental results is still very difficult since nucleation, attrition, agglomeration, and growth all influence one another and largely determine the product properties. Nevertheless, simplified models exist for all partial steps. These can predict the mechanism predominating at given supersaturation for a range of sub stances. The models presented permit calculation of the rate-determining kinetics over a wide range or, given a knowledge of the metastable range, permit prediction of a maximum rate of agglomeration, nucleation, and growth. This can be considered in estimation of the expected particle sizes. Based on the kinetics and giving due consideration to the demonstrated mutual interactions, the order of magnitude of important operating parameters for desired product properties, such as the optimum supersaturation, can be determined.