This book introduces the principles and mechanisms of the biological synthesis of nanoparticles from microorganisms, including bacteria, fungi, viruses, algae, and protozoans. It presents optimization processes for synthesis of microbes-mediated nanoparticles. The book also reviews the industrial and agricultural applications of microbially-synthesized nanoparticles. It also presents the medical applications of green nanoparticles, such as treating multidrug-resistant pathogens and cancer treatment. Further, it examines the advantages and prospects for the synthesis of nanoparticles by microorganisms. Lastly, it also presents the utilization of microbial-synthesized nanoparticles in the bioremediation of heavy metals.