Efficient ice slurry generation systems continuously produce ice crystals of desired size offering high cooling rates without any wall freeze-up. Although several ice slurry generation technologies have been and are being developed, currently only the scraped surface and supercooling type have been widely used in commercial applications. Typical ice slurry generators require the use of mechanical devices such as scraper blades, orbital rods or impacting solid particles to maintain a freeze-free ice-generating surface and achieve a continuous ice slurry production. The basic principles, operating ranges and heat transfer characteristics of the scraped surface and fluidized bed type ice slurry generators are reviewed. From this review it became clear that the basic crystallization principles and heat transfer mechanisms in current ice generators are not yet fully understood. To elucidate the heat transfer mechanisms, heat transfer measurements are presented in a prototype compact ice generator.