ABSTRACTThere is an increasing demand for simple, greener, and cost-effective synthesis of nanomaterials and nanostructures with well-defined and uniform architectures. Recently, various studies are focused on the application of plant viruses and bacteriophages to construct innovative nano-based systems and nanoformulations; these viruses can be employed as suitable scaffolds or biotemplates for nanoparticle synthesis in view of their structural symmetry, simplicity in functionalization/surface modification, small sizes, various distinct shapes, simple genetic manipulation, monodispersity, and capability of self-assembling. Additionally, plant viruses and bacteriophages with their unique structures and relative simplicity have shown attractive advantages such as ease of isolation or purification processes and nonpathogenicity to humans and animals. However, there is still a lack of knowledge regarding the mechanisms and relative processes of nanoparticle formation using these viruses. Notably, host organisms are required for protein expression, and there are limited studies on optimization of nanoparticle synthesis and up-scalable and commercial production; therefore, more elaborative studies and comprehensive evaluations should be conducted to find and solve these challenging issues. In this review, important matters pertaining to viral fabrication of nanoparticles using plant viruses and bacteriophages are covered, with a focus on possible mechanisms and related important challenges.