It is shown for the first time that a combination of molecular simulations and process modeling can be used to predict crystalline product quality aspects such as the polymorphic fraction and crystal size distribution. Using molecular simulations the interfacial energy of 2D nuclei and the step free energy of 2D nuclei on crystal surfaces of different polymorphs are determined. These result in the nucleation and growth behavior of the polymorphs as a function of the supersaturation. The supersaturation development during polymorph crystallizations can be accounted for using dynamic process modeling. Furthermore, this study clearly demonstrates that a deeper understanding of polymorph crystallization can be obtained by combining research on a molecular scale with that on a process scale. Molecular simulations show, for instance, that there is no simple relationship between experimental solubility and apparent interfacial energy of the polymorphs.