Adjuvants are substances that are added to vaccines to enhance the body's immune response to the vaccine antigens. They help stimulate the immune system and improve the overall effectiveness of the vaccine by triggering a stronger and longer-lasting immune response. Adjuvants can be classified into different types based on their mechanism of action, such as aluminum salts, oil-in-water emulsions, and liposomes. Research in this area focuses on understanding how adjuvants can boost the immune response to vaccines, developing new adjuvants with improved efficacy and safety profiles, and investigating their potential use in novel vaccine formulations against various infectious diseases and cancers.