Industrial crystallization for the production of desired products, as expressed by produced crystal size and production rate, is discussed theoretically, and effective secondary nucleation and crystal growth rate are shown to be important. Recent studies on secondary nucleation rates are reviewed that involve complicated mechanisms and considered for application in design of crystallizers, Sticking phenomenon of suspended fines on growing crystals is discussed with regards to the population density of fines on the surface of growing seed, New mechanisms of crystal growth in an industrial crystallizer are also reviewed that involve breakage of growing crystal and sticking of suspended fines, and crystal growth rates available to calculate seating up of a crystallizer is discussed. Two kinds of design theories of continuous crystallizers are reviewed, One is proposed on an ideal models of states of crystal and solution in a crystallizer and the dimensionless characteristic factors defined by dimensionless crystal size and supersaturation, can be used, independently of system and product crystal size and shape. Another theory is proposed on product crystal, and Is shown to be applicable to operational line, independently of size of a crystallizer under some restricted conditions. Finally, industrial crystallization is becoming more and more important not only in conventional mass chemical processes, but also in fine chemical ones, and progressive studies on industrial crystallization will answer to the needs of the chemical industries in future.