A population balance model for predicting the dynamic evolution of crystal shape distribution is further development to simulate crystallization processes in which multiple crystal morphological forms co-exist and transistions between them can take place. The new model is applied to derive the optimal temperature and supersaturation profiles leading to the desired crystal shape distribution in cooling crystallization. Since tracking an optimum temperature or supersaturation trajectory can be easily implemented by manipulating the coolant flowrate in the reactor jacket, the proposed methodology provides a feasible closed-loop mechanism for crystal shape tailoring and control. The methodology is demonstrated by applying it to a case study of seeded cooling crystallization of potash alum. (C) 2009 American Institute of Chemical Engineers AIChE J. 55: 2049-2061, 2009