Wet classification has been challenged during the last years to produce efficiently size distributions which either very fine or very narrow. This has reflected both in the optimization of existing classification methods and in the research of new equipment. Classification modelling has emerged a new era with the increasing use of sophisticated models, both phenomenological and based on hydrodynamic simulations. Also the normal empirical and semi-empirical models have been in recent years validated, Hydrocyclones are being used in many different fine applications and processes, New classification techniques have emerged to produce very fine products.