The shape of a crystalline solid has a major impact on its downstream processing and on its end-use properties and product functionality, issues that are becoming increasingly important in the pharmaceutical and life science, as well as the specialty and ¯ne chemical industries. Though it is widely known that improved crystal shapes can be achieved by varying the conditions of crystallization (e.g., solvent type, additive and impurity levels, etc), there is far less understand- ing of how to effect such a change. Until recently, most methods for predicting crystal shapes were based exclusively on the internal crystal structure, and hence could not account for solvent or impurity effects. New approaches, however, over the possibility of accurately predicting the effects of solvents. We review models for predicting crystal shape, and evaluate their utility for process and product design.