As an eco-friendly method of preparing nanoparticles with reduced toxicity toward organisms and the environment, green synthesis is gaining importance. Nanotechnology can be used in an eco-friendly manner to translate green chemistry principles and engineering into useful nano-products. Plants and microbes can synthesize nanoparticles to counteract many advantages. In addition to energy savings, green synthesis can reduce production costs and reduce environmental waste, which will benefit the commercial-scale production of nanoparticles. It has been found that phytochemicals and biomolecules derived from plants and microbes can be used to reduce particle size and stabilize particles. Green synthesis of nanomaterials has different advantages of reducing toxic metal substances into nontoxic products with well-defined structure, shape, and size, which can be used to treat cancer, fight infections, neutralize fungal growth, etc. This chapter focuses on the molecular mechanisms of biosynthesis of different nanoparticles (NPs) from plants and microorganisms and their biomedical efficacy such as health and medicine due to their eco-friendly properties to be discussed. © 2024 Elsevier B.V., All rights reserved.