Nanoparticle synthesis under environmentally friendly conditions has been conducted utilizing natural resources in order to reduce the reliance on hazardous chemicals. For example, the utilization of microbial synthesis has enabled the production of nanoparticles that exhibit biocompatibility, stability, and safety. Microorganisms facilitate the growth of crystals while preventing aggregation. They serve as both reducing agents and capping agents by offering enzymes, peptides, poly(amino acids), polyhydroxyalkanoate, and polysaccharides. In this review, we present an overview of nanoparticle synthesis based on microorganisms including bacteria, fungi, algae, and actinobacteria, encompassing metals such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd), copper (Cu), titanium dioxide ((TiO₂), zinc oxide (ZnO), iron oxide (Fe₂O₃), and selenium (Se). The nanoparticles typically vary in size from 1 to 100 nm and exhibit various shapes including spherical, rod-shaped, triangular, cubic, and hexagonal shapes. Additionally, this review discusses the mechanisms behind the synthesis of metal nanoparticles by microorganisms, whether they occur intracellularly or extracellularly.