Preclinical studies have shown promising results for cancer immunotherapies that use nanoparticles derived from plant viruses (PVNPs). These nanoplatforms can act as both endogenous immune adjuvants and nanocarriers for exogenous immune adjuvants and cancer antigens. Although they do not infect mammalian cells, PVNPs are still recognized by pathogen pattern recognition receptors (PRRs) in different ways, as they are viruses. This recognition leads to the activation of antigen-presenting cells (APCs) and other innate immune cells, which in turn stimulates the expression of costimulatory molecules. These PVNPs can be used in innovative cancer immunotherapy approaches, such as in situ vaccines (ISVs), to inhibit tumor growth after intratumoral delivery and to boost systemic anticancer immunity. PVNPs can also enhance both local and systemic anti-tumor immune responses when combined with other tumor immunotherapeutic strategies and other forms of cancer treatment.