Microfluidic droplet-based systems represent a unique tool to study crystallization kinetics as they allow a precise temperature control,few impurities and the possibility to control fluid dynamics.Cooling crystallization from solution is widely used in pharmaceutical industry for producing and purifying Active Pharmaceutical Ingredients(API).API crystals have to meet many specifications in terms of purity and size distribution.For this reason,an accurate knowledge of the crystallization process is necessary.The first,critical step of crystallization is nucleation,where molecules in solution form unstable aggregates which may eventually grow to stable nuclei and form crystals.