Adjuvants are chemicals, microbial components, or mammalian proteins that enhance the immune response to vaccine antigens. Reducing vaccine-related adverse effects and inducing specific types of immunity has led to the development of numerous new adjuvants. Adjuvants in experimental and commercial vaccines include aluminum salts (alum), oil emulsions, saponins, immune-stimulating complexes (ISCOMs), liposomes, microparticles, nonionic block copolymers, derivatized polysaccharides, cytokines, and a wide variety of bacterial derivatives. The mechanisms of action of these diverse compounds are different. Factors influencing the selection of an adjuvant include animal species, specific pathogen, vaccine antigen, route of immunization, and type of immunity needed. In this paper we review the current adjuvant types, structure and mechanism of action and their application in the design and production of animal and human vaccines to provide a source for students and researchers in related fields .