Green synthesis of metal oxide nanoparticles using plant extracts has emerged as a sustainable and environmentally friendly alternative to conventional chemical and physical synthesis methods. This review comprehensively examines recent advances in plant-mediated biosynthesis of various metal oxide nanoparticles, including zinc oxide, titanium dioxide (TiO₂ ), iron oxide (Fe₂ O₃ /Fe₃ O₄ ), copper oxide, and other metal oxides. The mechanisms involving phytochemicals such as flavonoids, terpenoids, alkaloids, phenolic compounds, and saponins as reducing and stabilizing agents are discussed in detail. Characterization techniques including UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy are reviewed. Applications of green-synthesized MONPs in environmental remediation, biomedical fields, photocatalysis, antimicrobial activity, and agricultural practices are highlighted. The advantages of plant-based synthesis over microbial and chemical methods, including cost-effectiveness, scalability, and reduced environmental impact, are emphasized. Future perspectives and challenges in standardization, mechanistic understanding, and industrial translation are also addressed.