The global spread of infectious diseases has raised public awareness of vaccines, highlighting their essential role in protecting public health. Among the components of modern vaccines, adjuvants have received increasing attention for boosting immune responses and enhancing efficacy. Recent advancements in adjuvant research, particularly nanodelivery systems, have paved the way for developing more effective and safer adjuvants. This review outlines the properties, progress, and mechanisms of FDA-approved conventional adjuvants, focusing on their contributions to and challenges in vaccine success. Despite these advancements, conventional adjuvants still face suboptimal immunomodulatory effects, potential side effects, and limitations in targeting specific immune pathways. Nanodelivery systems have emerged as a transformative approach in adjuvant design, offering unique advantages such as enhancing vaccine stability, enabling controlled antigen release, and inducing specific immune responses. By addressing these limitations, nanocarriers improve the safety and efficacy of conventional adjuvants and drive the development of next-generation adjuvants for complex diseases. This review also explores strategies for incorporating nanodelivery systems into adjuvant development, emphasizing its role in optimizing vaccine formulations. By summarizing current challenges and recent advances, this review aims to provide valuable insights guiding future efforts in designing innovative adjuvants that meet the evolving needs of global immunization programs.