Developments of crystallization operation in chemical industries are summarized and recent studies in the United States, Europe and Japan are introduced. Especially, development of design theories of crystallizers is discussed in relation to crystallization phenomena of crystal growth and nucleation rate in a crystallizer. Average crystal growth rate used for calculating product crystal size and production rate in a crystallizer, is discussed in comparison with linear growth rate of a single crystal. These design theories have made crystallization processes popular in chemical industries. New crystallization processes have been developed for special purposes concerned with new separation methods under low consumption of energy, new processes for product characterized by high purity and special properties, new technology for prevention of water polution, and others. And also new type crystallizers have been studied for these processes. As these crystallization technology have been developed, new research themes have emerged. Behaviors of fines in a supersaturated solution are discussed based on the results newly obtained on nucleation and growth rate, considering chemical industrial operations, as an example.