Polymer nanocomposites (PNCs) are advanced materials that improve the mechanical, thermal, electrical, and barrier properties of polymer matrices by incorporating nanoparticles into them. To define the structure-property correlations and overall performance of PNCs, synthesis is essential. Depending on the kind of polymer, nanofiller, and intended use, there are several synthesis techniques that offer unique advantages. One popular method is in situ polymerization, in which nanoparticles are first distributed throughout a monomer solution. The uniform distribution of nanofiller and enhanced material properties are the outcomes of this technique, which fosters strong interfacial interactions. Another popular method is solution mixing, which involves dispersing nanoparticles in a polymer solution and then letting the solvent evaporate. Processing conditions and solvent compatibility may limit its ability to achieve good dispersion. By employing high shear mixing to incorporate nanoparticles into a polymer melt, melt blending is a solvent-free, eco-friendly method. Although it can have problems with nanoparticle aggregation, this technique offers good scalability and is compatible with thermoplastic polymers. In order to create well-distributed nanocomposites with more morphological control, emulsion polymerization involves polymerizing monomers in an aqueous solution with surfactants and scattered nanoparticles. Advanced methods include layer-by-layer (LbL) assembly, which provides exact control over nanofiller placement at the nanoscale, and electrospinning, which produces polymer nanocomposite fibers with a large surface area. Additionally, recent developments explore sol-gel processing for hybrid organic-inorganic nanocomposites, which achieve remarkable interfacial adhesion and dispersion. The characteristics, processing viability, and scalability of the nanocomposite for industrial applications are all significantly impacted by the synthesis method choice.