Aluminum-containing adjuvants are an important component of many vaccines because they safely potentiate the immune response. The structure and properties of aluminum hydroxide adjuvant, aluminum phosphate adjuvant and alum-precipitated adjuvants are presented in this review. The major antigen adsorption mechanisms, electrostatic attraction and ligand exchange, are related to the adjuvant structure. The manner by which aluminum-containing adjuvants potentiate the immune response is related to the structure, properties of the adjuvant and adsorption mechanism. Immunopotentiation occurs through the following sequential steps: inflammation and recruitment of antigen-presenting cells, retention of antigen at the injection site, uptake of antigen, dendritic cell maturation, T-cell activation and T-cell differentiation.