Nanoparticles and nanocrystals have emerged as important areas in the development of diverse industries, including pharmaceuticals, agriculture, and electronics, due to their unique properties and wide-ranging applications. In this chapter, the crystallization process was discussed through the lens of classical nucleation theory and transitions to nanocrystallization with a focus on spatial and time confinement. Both top-down and bottom-up techniques can be used in the production of nanoparticles and nanocrystals; however, bottom-up methods such as sol–gel processing, aerosol techniques, and chemical vapor deposition often face limitations in achieving precise control over crystallinity. Techniques like spray drying, non-thermal plasma synthesis, and membrane-assisted crystallization address the challenges of those methods by enabling the production of high-quality nanocrystals with enhanced structural control. For large-scale production, process intensification strategies, such as reactive crystallization, ultra-sound assisted crystallization, and continuous crystallization aim to optimize energy consumption while enhancing product yield and consistency. The integration of in-situ monitoring systems, Process Analytical Tools (PATs), and microfluidic technology have made a rapid shift from traditional batch crystallization to efficient continuous systems by providing improved control over nucleation, growth, and crystallization kinetics, effectively bridging the gap between laboratory-scale to industrial-scale applications.