The sustainable synthesis of polymer nanocomposites (PNCs) has gained considerable recognition for its emphasis on environmentally friendly materials, energy-efficient methods, and the use of renewable resources. Innovations in green chemistry have paved the way for creating PNCs using natural polymers such as cellulose, chitosan, starch, alginate, and collagen, alongside biobased nanofillers like montmorillonite, silica nanoparticles, cellulose nanofibers, and lignin nanoparticles. These renewable materials not only minimize environmental impact but also improve the biodegradability of the resulting composites. Recent developments have highlighted the adoption of green methodologies that enhance the performance and efficiency of PNCs. Techniques such as microwave-assisted synthesis and ultrasonic processing have been optimized to reduce energy consumption and production time while ensuring better dispersion of natural nanofillers within polymer matrices. Mechanochemical approaches, which avoid the use of solvents, have seen notable advancements, and ionic liquid-based synthesis is now more adept at controlling nanoparticle size and uniformity. Furthermore, supercritical fluid processing has emerged as an effective way to improve material properties without relying on harmful solvents. The use of plant extracts, microbial processes, and enzymatic catalysts in the synthesis of nanofillers is gaining momentum due to their renewable and non-toxic attributes. In situ polymerization techniques, which enable direct formation around nanofillers, ensure even distribution and eliminate the need for additional processing steps. Moreover, integrating renewable energy sources, such as solar energy, to drive synthesis reactions is becoming a promising strategy to reduce overall energy demands. This chapter delves into these advanced green techniques, offering a comprehensive overview of their applications and benefits.