Nanotechnology, especially the development of nanoparticles (NPs), has revolutionized diverse fields including medicine, agriculture, and environmental science. Polysaccharide-based nanoparticles (PNPs) have gained significant interest due to their natural origin, biocompatibility, biodegradability, and functional versatility. Derived from sources such as plants, algae, animals, and microbes, polysaccharides like chitosan, alginate, starch, and cellulose serve as green alternatives in nanoparticle synthesis. These biopolymers offer abundant reactive groups such as hydroxyl, carboxyl, and amino that enable efficient binding and functionalization, eliminating the need for toxic reagents. Various fabrication techniques, including ionic gelation, nanoprecipitation, and electrospinning, allow for the synthesis of tailored PNPs with specific size, morphology, and surface characteristics. Functionalization approaches, such as ligand conjugation, PEGylation, and covalent crosslinking, further enhance the stability, targeting ability, and therapeutic efficacy of these nanomaterials. Surface modification plays a vital role in optimizing drug delivery, diagnostics, and tissue regeneration applications. Extraction and purification of polysaccharides from natural sources are critical for ensuring the quality and performance of the resulting nanoparticles. The unique physicochemical and biological properties of PNPs, including controlled release behavior, mechanical strength, and biocompatibility, position them as vital tools in modern nanomedicine and environmental sustainability. As research advances, the development of smart, stimuli-responsive, and eco-friendly PNPs is expected to drive innovations in targeted therapeutics and sustainable material science.