Most traditional models of wet granulation processes use one-dimensional population balances, which assume that granule size is the only independent granule property that significantly affects granule growth behaviour. However, several other independent granule properties have been identified. which can also strongly influence granulation behaviour. These include granule binder content, porosity, and primary particle size distribution and composition. Most population balance models also implicitly assume that conditions are spacially uniform throughout the granulator. However, segregation has the potential to occur in many commercial granulators. This will alter the frequency and velocity of collisions between different sizes of granule. Hence, current one-dimensional models of wet granulation are inadequate. These models need to be expanded to three or four dimensions to include size. porosity, binder content, and composition (where applicable) as independent granule properties and also need to include the effects of mixing and segregation within the granulator,