The emergence of polymeric nanoparticles (PNPs) as a promising platform for drug delivery, vaccine development, and genetic therapy encompasses superior bioavailability, targeted delivery, and controlled release. Most importantly, PNP has the potential to facilitate the delivery of small molecules, peptides, proteins, and nucleic acids against the special barriers of poor solubility, immune clearance, and endosomal escape. Advances in multi-stimuli responsive systems (MRS) and artificial intelligence (AI)-assisted drug design have further enhanced their potential. Despite such great potential, manufacturing challenges still exist on a large scale, through stability, and regulatory landscapes that need to be negotiated. The case studies of approved PNP-based therapeutics illustrate both potential opportunities and complexities for the development and marketability of such systems. This chapter discusses the basic principles, fabrication methods, encapsulation strategies, and pharmacokinetic profiles that make PNPs effective in biopharmaceutical applications. Further research efforts will focus on biodegradable polymers (BDPs) for tailored medicine applications, smart drug delivery systems, and regulatory standardization to maximize clinical utility while ensuring their safety and efficacy.