NanomaterialsNanomaterial exhibit unique propertiesProperties distinct from their bulk counterparts, particularly due to their high surface-to-volume ratioSurface-to-volume ratio, and the quantum confinement effectQuantum confinement effect. Controlling the sizeSize and shapeShape of nanoparticles (NPsNanoparticles (NPs)) is essential for developing advanced applicationsApplications. Two main synthesisSynthesis approachesApproach are commonly employed: top-downTop-down and bottom-upBottom-up. While top-down methodsMethods are energyEnergy-intensive and less suitable for producing biological NPsNanoparticles (NPs), bottom-upBottom-down techniquesTechnique often rely on chemical reagents that can generate environmentally harmful byproducts. In contrast, biological synthesisBiological synthesis using microorganismsMicroorganisms or plant extractsPlant extract offers advantages such asNanotechnology and environmental sustainability environmental sustainabilityEnvironmental sustainability, non-toxicityToxicity, and cost-effectiveness. MicrobialMicrobial biomoleculesBiomolecule, such as proteinsProtein, carbohydratesCarbohydrate, lipidsLipids, nucleic acidsNucleic acid, polysaccharidesPolysaccharide, and enzymesEnzyme act as reducing, stabilizing, and capping agents in the formation of metalMetal and metalMetal oxide NPsNanoparticles (NPs). Similarly, plant extractsPlant extract, which contain a complex mixture of biomoleculesBiomolecule (e.g., polysaccharidesPolysaccharide, proteinsProtein, amino acids, organicOrganic acids, polyphenols, flavonoids, terpenoids, alkaloids, tannins, and alcoholic compounds), can facilitate NPNanoparticles (NPs) formation, while also imparting additional bioactivity, making them suitable for diverse applicationsApplications inNanotechnology in medicine medicineMedicine, agricultureAgriculture, and environmental remediationEnvironmental remediation. Biosynthesized NPsNanoparticles (NPs) have shown promise in various in vitro and in vivo applicationsApplications, including antibacterial, antifungal, and anticancerAnticancer activities, as well as serving as photocatalysts for dye degradation and wastewater treatment. This chapter explores the synthesisSynthesis of metalMetal and metalMetal oxide NPsNanoparticles (NPs) using various biological agents such as bacteriaBacteria, fungiFungi, and plants, along with a discussion on their characterizationCharacterization and practical applicationsApplications.