Nanotechnology is a new approach for the production of particles with unique features at the nanoscale dimensions. Among the various routes available for the synthesis of these nanoparticles, biogenic synthesis is a simple, low-cost, and eco-friendly method. The biosynthesis of gold nanoparticles is provided by various natural sources including plants, fungi, bacteria, actinomycetes, yeasts, and algae. Gold nanoparticles of various shapes and sizes are synthesized using biomass and/or extract of the organism. Enzymes secreted by microorganisms and metabolites of plants act as reducing, stabilizing, and capping agents for the production of the nanoparticles. The gold nanoparticles have antibacterial/antifungal properties that can be used to protect plants against pathogens. In addition, they can be applied for pesticide identification and water purification. This chapter focuses on the biosynthesis of gold nanoparticles, their characterization, and application in agriculture.
