Any change in the synthesis method of polymeric nanoparticles requires a high number of experiments to capture all aspects involved. Understanding the role of transport phenomena, however, makes it possible to relate the particle properties to the operating conditions,and allows extrapolating the results to different systems and operating conditions using a few additional experiments. Examples of this approach, related to the production and preservation by freeze-drying of the nanoparticles, are shown in this chapter, focusing on nanospheres and nanocapsules obtained by solvent displacement in intensive mixers. In particular, it will be shown how it is possible to correlate the final size of the nanoparticles, a critical parameter for parenteral applications, with process conditions (polymer concentration, and type, flow rate in the synthesis apparatus, etc.). Examples with different polymers, polymers of different molecular weight and solvents are shown. Finally, the transfer process and scale up from lab to production units are discussed.