This review discusses the green synthesis of metallic nanoparticles using biological entities such as microorganisms and plants. Nanotechnology involves manipulating materials at the nanoscale (1-100 nm), where unique properties emerge. Traditional methods often use toxic chemicals, but biological synthesis offers an environmentally friendly alternative. Nanobiotechnology uses biological entities like bacteria, fungi, plants, and viruses to synthesize nanoparticles, which can be used in various applications, including medicine, electronics, and catalysis. The review highlights the advantages of biological synthesis, including cost-effectiveness, safety, and the ability to produce nanoparticles with controlled size and shape. It covers characterization techniques such as UV-vis spectroscopy, TEM, SEM, and XRD to analyze nanoparticle properties. The review also discusses the synthesis of various nanoparticles, including gold, silver, copper, copper oxide, palladium, and platinum, using different biological entities. Factors influencing nanoparticle synthesis, such as pH, temperature, and reaction time, are discussed. The review emphasizes the potential of plant-based synthesis due to its simplicity, cost-effectiveness, and scalability. It also highlights the antimicrobial and catalytic properties of nanoparticles synthesized using biological methods. The review concludes that biological synthesis is a promising approach for producing nanoparticles in an environmentally friendly and sustainable manner.This review discusses the green synthesis of metallic nanoparticles using biological entities such as microorganisms and plants. Nanotechnology involves manipulating materials at the nanoscale (1-100 nm), where unique properties emerge. Traditional methods often use toxic chemicals, but biological synthesis offers an environmentally friendly alternative. Nanobiotechnology uses biological entities like bacteria, fungi, plants, and viruses to synthesize nanoparticles, which can be used in various applications, including medicine, electronics, and catalysis. The review highlights the advantages of biological synthesis, including cost-effectiveness, safety, and the ability to produce nanoparticles with controlled size and shape. It covers characterization techniques such as UV-vis spectroscopy, TEM, SEM, and XRD to analyze nanoparticle properties. The review also discusses the synthesis of various nanoparticles, including gold, silver, copper, copper oxide, palladium, and platinum, using different biological entities. Factors influencing nanoparticle synthesis, such as pH, temperature, and reaction time, are discussed. The review emphasizes the potential of plant-based synthesis due to its simplicity, cost-effectiveness, and scalability. It also highlights the antimicrobial and catalytic properties of nanoparticles synthesized using biological methods. The review concludes that biological synthesis is a promising approach for producing nanoparticles in an environmentally friendly and sustainable manner.