Poor aqueous solubility remains a critical barrier in the development of many active pharmaceutical ingredients (APIs), with nearly 70% of drug candidates exhibiting limited dissolution rates and reduced bioavailability. Solid drug nanoparticle-based drug delivery has emerged as a transformative strategy to address these challenges, leveraging size reduction to enhance dissolution rates and solubility as described by the Noyes–Whitney and Ostwald–Freundlich principles. This chapter provides a comprehensive overview of nanoparticle production strategies, focusing on both top–down (wet milling, high-pressure homogenization) and bottom-up (crystallization and precipitation) approaches. While top–down techniques have dominated commercial applications, they are constrained by energy-intensive processing and potential thermal degradation. Conversely, bottom-up methods offer advantages in cost efficiency and scalability, but present challenges in particle size control, amorphous content, and long-term stability. Strategies for overcoming these limitations, including the use of stabilizers and advanced isolation methods such as spray drying, freeze drying, and supercritical fluid technologies, are critically discussed. By highlighting recent advancements in manufacturing and stabilization, this chapter emphasizes the pivotal role of drug nanoparticles in shaping next-generation pharmaceutical formulations and underscores the need for continued innovation to achieve effective, stable, and scalable delivery systems.