A new generation of smart nanocarriers offers excellent safety, efficiency, and targeted drug delivery for cancer immunotherapy. Conventional cancer treatments, such as radiation and chemotherapy, are often associated with severe systemic toxicity and extensive collateral damage to healthy tissues. In contrast, the enhanced permeability and retention effect and active targeting mechanisms of certain nanocarriers, such as liposomes, dendrimers, polymeric nanoparticles, and lipid-based systems, enable precise drug delivery. Therapeutic agents can be encapsulated within nanoscale delivery systems, protected from early degradation, and released in response to specific signals within the tumor microenvironment, such as changes in pH or enzyme concentrations. Targeting accuracy is further improved through surface modifications, including ligands, antibodies, or aptamers, which facilitate intracellular uptake and mitigate off-target effects. Additionally, the wide variety of nanocarrier structures available—from polymersomes and micelles to nanospheres and nanocapsules—allows customized applications tailored to different cancer types and stages. Current research highlights the potential for immunomodulatory drugs loaded into nanocarriers to enhance antitumor immunity and overcome mechanisms of immunoresistance. This review discusses the classification, processes, and biological applications of smart nanocarriers, with particular emphasis on how they can advance cancer immunotherapy by addressing challenges related to drug loading, targeted delivery, and biocompatibility.