The utilization of immunomodulatory nanomaterials, i.e., leveraging their unique properties to enhance immune responses, represents a transformative approach for the treatment of various diseases. Recent advancements in nanotechnology have enabled the design of nanomaterials capable of delivering immunomodulatory agents in a targeted manner, such as cytokines, antibodies, and nucleic acids, to specific cells or tissues involved in immune regulation. These nanomaterials, including nanoparticles, liposomes, nanogels, nanoemulsions, dendrimers, MXenes and extracellular vesicles, have been increasingly tailored to modulate immune responses with precision and efficacy. This targeted approach not only enhances therapeutic outcomes but also reduces off-target effects, minimizing systemic toxicity. In this review, an overview of immunomodulatory nanomaterials and their biomedical applications are highlighted. Herein, we have discussed different types of nanomaterials and their design strategies, interactions with different immune system components (macrophages, dendritic cells (DCs), neutrophils, T lymphocytes (CD4⁺ helper T-cells, CD8⁺ cytotoxic T-cells, regulatory T-cells/Tregs, and memory T-cells), and B lymphocytes), and immunomodulation mechanisms. Furthermore, nanomaterial-based immunomodulation strategies to enhance cancer immunotherapy, wound healing, and bone regeneration and the treatment of infectious diseases, autoimmune diseases, and allergy and are discussed in detail. In addition to therapeutic applications, selected nanomaterial platforms demonstrate significant potential in pharmaceutical formulations by improving drug stability, controlled release, and bioavailability, as well as in cosmetology through skin-targeted delivery, anti-inflammatory activity, immune protection, and enhanced tissue regeneration. Finally, clinical trial updates, challenges and future prospects are outlined. Key findings indicate that lipid-based, polymeric, inorganic nanoparticles and dendrimers provide complementary advantages for immunomodulation, including efficient delivery, controlled release, multifunctionality, and precise immune targeting. Despite safety, regulatory, and scalability challenges, these systems show strong potential for advancing precision and personalized medicine. Taken together, these innovations hold great promise for personalized medicine approaches, wherein nanomaterials can be tailored to individual patient profiles for more effective and precise disease treatment and prevention strategies. This review focuses primarily on the mechanistic interactions between immunomodulatory nanomaterials and immune cells, including macrophages, dendritic cells, neutrophils, T lymphocytes, and B lymphocytes, rather than providing an exhaustive treatment of physicochemical optimization parameters such as particle size or surface modification chemistry, which fall outside the defined scope of this work.