Contributions to industrial crystallization up to the 70s were dominated by items like crystallizer design. A major advance in the field came with the introduction of the population balance by Randolph and Larson.In the resulting research, the topic of secondary nucleation was important since the tool of "population density balance" brought this field of crystallizer design into focus. The study of secondary nuclei resulted in the theory of growth rate dispersion (GRD), which was the centre of scientific papers of the time.It was proved that there is no size dependent growth, the explanation coming from GRD and (more importantly) the fact that larger crystals have a higher thermal velocity and therefore a thinner boundary layer and therefore a better heat and mass transfer (a higher growth rate).The introduction of the three step model, contrary to the commonly used two step model in solution crystallization, was an important step forward in understanding of crystal growth.From the above research it was shown that dissolution is exactly the opposite phenomenon of crystal growth. Dissolution shows the three steps: surface disintegration, diffusion through the boundary layer and a heat transfer term. Also a process like dissolution rate dispersion exists. Often, however, not all of those steps are visible since they are frequently much faster than in the case of crystal growth.There are three clear new trends in this field of research. The first is crystallizer control, with the aim of better crystals (shape, size distribution, purity) by means of measuring supersaturation and crystal sizes in-line/on-line. Here sensor development is a key issue.The second trend is the molecular modeling of crystals. The focus is on finding "tailor made additives" by computer simulations. The additive should influence the crystal shape to help the post crystallization operations like solid-liquid separation or the solid handling. The computer simulation should save time and lower laboratory costs. This research field has opened due to the fast development of hardware and software in computer science in the last 20 years.The third trend is for a more detailed view and control of polymorphism and pseudo polymorphism of the crystallized substances. The last point is of course important in the field of pharmaceuticals and food, and the increase in crystallization research within these fields compared to ten or twenty years ago is marked.