Viruses infecting higher plants have been the subject of intense study for over a century, a plant virus being the first virus ever described, even providing the name for the new class of microbes. Most plant viruses cause diseases in infected plants. As in most other areas of Virology, this pathogenic aspect of the relationship of viruses with their hosts has been the main driving force guiding virus studies. However, in addition to their pathogenic side, viruses are endowed with other biotechnologically significant properties. For instance, viruses are intracellular replicating machineries, being able to accumulate to very high levels within the infected cell. This accumulation takes place in the form of virus-induced natural nanoparticles called virions, which are cages containing the viral genome. Notably, technology has been developed allowing the intracellular generation of viral cages not containing nucleic acids (so-called ‘virus-like particles’ or VLPs). VLPs derived from plant viruses are plant-made nanoparticles which can be produced at high levels and which are amenable to experimental manipulation in many directions. Since actual viruses are also nanoparticle-inducers (virions), the ‘umbrella’ term of ‘viral nanoparticles’ (VNPs) has been coined to include all forms of virus-derived nanoparticles. VNPs can be viewed from a nanotechnological standpoint. VLPs can be used to encapsulate a variety of other molecules, such as drugs, proteins of all sorts, image enhancers, etc. Parts of their external surfaces can be substituted with other molecules, the whole surface can be decorated with new molecules, and avidity for new interactions between the VNPs and other molecules, or even other nanoparticles, can be created. The more classical ´molecular farming´ goal of making plants serve as natural biofactories has now been enlarged to compass their use as factories for the production of custom-made nanoparticles, the modified VNPs. Applications of this emerging technology are myriad. Biomedicine – both therapy and diagnosis-, agriculture, micro- and nanodevices, including electronic applications, environmentally-oriented developments are only the most obvious examples already found in the literature. Many more will undoubtedly emerge as the field grows. Indeed, with this technology plant biotechnology meets nanotechnology. In this Research Topic we welcome submissions on all on the different aspects of plant-made viral nanoparticles, ranging from basic structural studies of the different VNPs in connection with their applications, all the way to details of their practical implementation. Intermediate aspects, such as VNP construct engineering, production and purification issues, results obtained in their different applications, and overviews or reflections on the different technologies involved would enable coverage of all aspects of the topic.