Purpose <p>The increasing use of metal and metal oxide nanoparticles in industrial and biomedical applications has raised important environmental and health concerns. Conventional synthesis routes often depend on toxic chemicals and energy-intensive processes. This review aims to examine how isolated plant-derived polyphenols function as natural reducing and stabilizing agents in the green synthesis of nanoparticles, addressing the research question: <i>How do specific polyphenols influence nanoparticle formation</i>,<i> morphology</i>,<i> and applicability?</i></p> Methods <p>A comprehensive analysis of published experimental studies was conducted, focusing on isolated polyphenol classes such as flavonoids, tannins, lignans, and stilbenes. Mechanistic pathways of reduction and stabilization were examined, and the effects of synthesis parameters including polyphenol concentration, pH, and temperature on nanoparticle morphology were reviewed.</p> Results <p>Findings show that isolated polyphenols effectively mediate nanoparticle synthesis by reducing metal ions and stabilizing formed particles, enabling controlled size and shape formation. Variations in reaction conditions markedly influence nanoparticle morphology. Polyphenol-capped nanoparticles demonstrated enhanced biocompatibility and exhibited promising performance in catalysis, sensing, antimicrobial activity, and drug delivery applications.</p> Conclusion <p>Polyphenol-mediated nanoparticle synthesis offers a sustainable, efficient, and tunable alternative to conventional chemical methods. Despite its potential, challenges remain—including the standardization of plant extracts and the consistent isolation of specific polyphenols. Addressing these limitations will be essential to fully harnessing this green synthesis approach for advanced industrial and biomedical applications.</p>