Metallic nanoparticles have found wide applications due to their unique physical and chemical properties. Green biosynthesis using plants, microbes, and plant/microbial extracts provides an environmentally friendly approach for nanoparticle synthesis. This review discusses the mechanisms and factors governing the biosynthesis of metallic nanoparticles such as silver, gold, and zinc using various plant extracts and microorganisms, including bacteria, fungi, and algae. The phytochemicals and biomolecules responsible for reducing metal ions and stabilizing nanoparticles are discussed. Key process parameters like pH, temperature, and precursor concentration affecting particle size are highlighted. Characterization techniques for confirming the formation and properties of nanoparticles are also mentioned. Applications of biosynthesized nanoparticles in areas such as antibacterial delivery, cancer therapy, biosensors, and environmental remediation are reviewed. Challenges in scaling up production and regulating nanoparticle properties are addressed. Power Point 365 was used for creating graphics. Overall, green biosynthesis is an emerging field with opportunities for developing eco-friendly nanomanufacturing platforms using abundant natural resources. Further work on optimizing conditions, standardizing protocols, and exploring new biosources is needed to realize the full potential of this approach.