Nanoparticle-based drug delivery systems represent a transformative advancement in pharmaceutical science, offering precise control over drug release, improved bioavailability, and targeted therapeutic action. This chapter explores the functional properties of nanoparticles—including size, surface charge, morphology, and surface chemistry—and how these influence pharmacokinetics, biodistribution, and therapeutic efficacy. A detailed classification of nanoparticle types such as polymeric nanoparticles, liposomes, solid lipid nanoparticles, dendrimers, and micelles is provided, followed by a discussion on nanoformulations design considerations, including materials selection, stability, drug loading, and route-specific challenges. The chapter also covers essential characterization techniques, in vitro and in vivo evaluation models, regulatory pathways across global agencies (FDA, EMA, CDSCO), and emerging technologies such as AI-guided design and 3D printing. Through case studies and comparative analysis, the chapter underscores the critical interplay between nanoparticle design and clinical performance, concluding with a forward-looking discussion on the challenges and innovations shaping the next generation of nanomedicine.