The hydrothermal crystal growth has been discussed with respect to its evolution, current trends, intelligent engineering of the hydrothermal processes, apparatus used, safety issues involved followed by the hydrothermal processing of some selected crystals like quartz, berlinites, potassium titanyl phosphate, calcite, corundum, emerald, rare earth vanadates, native elements and simple oxides, sulfides, complex coordinated crystals of silicates, phosphates, vanadates, fine to nanocrystals, etc.