This paper reviews research work concerning the size distribution of product crystals in batch crystallization of well-soluble materials. The discussion was made with particular emphasis on seeding effect on product crystal size distribution and crystallizer performance. First, it is shown by a brief survey of the history of batch crystallization research that the importance of seeding in the performance of a batch crystallizer has been ignored while the importance of cooling profile (or supersaturation profile) had been overestimated. Then, the extensive research work carried out by the group of the present authors on seeding effect is reviewed, where the effectiveness of seeding in controlling product crystal size is clearly shown with experimental evidence. Specifically, it is shown that seed crystals added at the beginning of a batch can be grown with no generation of fine crystals if seed crystals are added enough over a critical seed loading ratio. Finally, recent research work in literature on batch crystallization is briefly surveyed.