Noble metal nanoparticles exhibit physicochemical properties that are not exhibited by either individual molecules or bulk metals. Physicochemical, optoelectronic and electromagnetic properties of nanoparticles are due to their large surface area and energy, spatial confinement and reduced imperfections, whereby size, shape and crystallinity determine their properties.

Presenting important applications, silver nanoparticles have become one of the most commercialized nanomaterials and can be obtained by several chemical, physical or biological methods. However, there is a preference for a biocompatible, non-toxic and eco-friendly method, and scientists began to steer their attention towards microorganisms as a source of biomolecules in nanobiotechnology. Plants, bacteria, algae, yeasts and filamentous fungi have been investigated and applied as a source for such bio-reductant and stabilizer molecules.

Accordingly, this chapter highlights the main aspects related to the intra- and extracellular biosynthesis of silver nanoparticles by fungi with several examples present in the literature. Analytical tools for physicochemical characterization of silver nanoparticles, mechanisms of synthesis, synthesis by marine fungi species as well as antimicrobial activity, cytotoxicity and bottlenecks of biological nanoparticle synthesis are laid out.