<p>Industrial effluents containing metal ions, dyes, and organic/inorganic pollutants significantly deteriorate groundwater quality. To address this, advanced, eco-friendly materials are needed for effective water purification. This study explores polymer nanocomposites (PNCs) as promising materials for wastewater treatment due to their large surface area and high adsorption/degradation efficiency. The hypothesis is that incorporating metal or metal oxide nanoparticles into polymer matrices enhances adsorption, thermal, and mechanical properties. This review evaluates the classification, fabrication, characterization, and application of PNCs across medicine, electronics, sensors, coating industry, aerospace, drug delivery, food industry, and environmental remediation. A comparative analysis of recent methodologies demonstrates significant progress beyond conventional nanomaterials, highlighting the unique physicochemical interactions that enhance adsorption, catalytic degradation, and mechanical properties. Furthermore, this review identifies key research gaps and presents an outlook on future innovations, including tailored nanocomposites, multifunctional hybrid materials, and scalable fabrication strategies. The insights presented herein contribute to the empirical literature by providing a comprehensive assessment of the evolving role of PNCs in addressing pressing environmental and industrial challenges. Results highlight their effectiveness in removing organic/inorganic pollutants and gas separations. The findings demonstrate the potential of PNCs for sustainable wastewater treatment and broader industrial applications.</p>