Recent advancements in green nanotechnology hold significant promise for transforming processes and products aimed at enhancing environmental quality, reducing pollution, safeguarding human health, and conserving both natural and nonrenewable resources. Recent research is actively involved to investigate the effective use of polymer nanoparticles synthesized through environmentally friendly techniques using plant extracts, enzymes, and bacteria. These approaches have applications in various fields, including electronics, biology, biomedicine, materials science, physics, environmental remediation, and interdisciplinary studies. The effectiveness of nanoparticles and its potential toxicity is largely hinge on their structural characteristics, including size, shape, composition, and surface chemistry, which are essential for achieving the desired results. This chapter explores in detail the synthesis, modification, and application of various natural polymer-derived nanoparticles in the context of green technology. It highlights the properties, challenges, functionalization approaches, and applications of natural polymeric nanoparticle delivery systems, which makes this chapter a unique one-stop resource for development. It also deals with the significant challenges in optimizing the effectiveness of natural polymer nanoparticle developments through green synthesis.