This book provides an account of the biogenic synthesis of nanomaterials by using different microorganisms. The chapters are focused on the biosynthesis of various metal and metal oxide nanosized materials by using bacteria, actinomycetes, fungi, and algae, including mechanisms of microbial synthesis. Other chapters summarize recent developments of microbial-based nanostructures for the management of food-borne pathogens, plant pathogenic fungi, as nutrients, and biomedical applications. Microorganisms are discussed not only as biofactories for the synthesis of nanomaterials but also as removal agents of toxic metals from the environment. Exposure sources and ecotoxicity of microbially synthesized nanoparticles are also discussed.