Crystallization is one of the oldest separation and purification unit operations which is widely used in processing of bulk commodities such as fertilizers, and specialty chemicals such as pigments and pharmaceutical products. In the former case, continuous multiple effect crystallizers in series are used, and in the latter case, batch and semi-batch crystallizers are utilized as reactive precipitation reactors. There are many types of crystallization processes and crystallizer types and many variables such as the concentration and type of impurities, the mode of operation, the degree of mixedness at molecular and bulk levels (leading to concentration and temperature gradients) that affect the crystal properties (crystal size distribution (CSD), crystal purity, and crystal shape). The aim of this document is to present, in a concise manner, issues related to modeling and control of crystallization processes from solution.