Rapid advancements in nanotechnology have brought innovative and transformative approaches to vaccine science; in this context, nanovaccines (nanovaxins) have begun to occupy a central place in modern immunization strategies. Nanovaccines are targeted, controlled, and highly effective vaccine platforms based on the delivery of antigens to the immune system via nanometer-scale carrier systems. These systems differ significantly from conventional vaccine technologies in that they increase antigen stability, allow for the simultaneous delivery of antigens and adjuvants, and can strongly induce both humoral and cellular immune responses. This book chapter comprehensively addresses the concept and fundamental principles of nanovaccines; the advantages offered by nanovaccines compared to classical vaccine systems are discussed at the molecular and cellular levels. Polymeric, lipid-based, inorganic, and biomimetic nanocarrier systems are examined in detail, and their effects on antigen delivery, cross-presentation, and immune response polarization are explained. Furthermore, the chapter highlights the crucial roles of biophysical parameters such as nanoparticle size, surface charge, morphology, and biodegradability in the efficacy and safety of nanovaccines. The chapter details the cellular mechanisms of action of nanovaccines, their interactions with antigen-presenting cells, and their capacity to activate the innate immune system; the translational value of this technology is demonstrated through current clinical and preclinical examples such as COVID-19 mRNA-LNP vaccines and cancer nanovaccines. Finally, by evaluating the safety, toxicity, and regulatory aspects of nanovaccines and future research directions, it is concluded that nanovaccines offer a promising vaccine paradigm in infectious diseases and cancer immunotherapy.