This review article focuses on the "green" synthesis of metal and metal oxide nanoparticles, emphasizing their applications in environmental remediation. Green synthesis is highlighted as a reliable, sustainable, and eco-friendly method for producing a wide range of materials, including metal/metal oxide nanoparticles, hybrid materials, and bioinspired materials. The article discusses the fundamental processes and mechanisms of green synthesis, particularly using natural extracts, and explores the role of biological components such as phytochemicals (flavonoids, alkaloids, terpenoids, amides, and aldehydes) as reducing agents and solvents. The stability and toxicity of nanoparticles, along with surface engineering techniques for achieving biocompatibility, are also covered. The applications of these synthesized nanoparticles in antimicrobial activity, catalytic activity, removal of pollutant dyes, and heavy metal ion sensing are discussed. The article concludes by emphasizing the potential of green synthesis in environmental remediation and other fields, while highlighting the need for further research to extend laboratory-based work to industrial scales.This review article focuses on the "green" synthesis of metal and metal oxide nanoparticles, emphasizing their applications in environmental remediation. Green synthesis is highlighted as a reliable, sustainable, and eco-friendly method for producing a wide range of materials, including metal/metal oxide nanoparticles, hybrid materials, and bioinspired materials. The article discusses the fundamental processes and mechanisms of green synthesis, particularly using natural extracts, and explores the role of biological components such as phytochemicals (flavonoids, alkaloids, terpenoids, amides, and aldehydes) as reducing agents and solvents. The stability and toxicity of nanoparticles, along with surface engineering techniques for achieving biocompatibility, are also covered. The applications of these synthesized nanoparticles in antimicrobial activity, catalytic activity, removal of pollutant dyes, and heavy metal ion sensing are discussed. The article concludes by emphasizing the potential of green synthesis in environmental remediation and other fields, while highlighting the need for further research to extend laboratory-based work to industrial scales.