An isolated ferritin fusion protein is provided in which ferritin is fused with a protein or peptide capable of being fused to ferritin without interfering with the polymeric self-assembly of the resulting fusion protein, and the protein may be of the endocapsid form when fused at the C terminus or an exocapsid form when fused at the N terminus. These fusion proteins may self-assemble into a variety of useful higher polymeric forms, e.g., capsid or other polymeric aggregate, and they are advantageous in that they are useful in a variety of applications, including human and veterinary vaccines and therapeutics, blood substitutes, image contrast agents, metal chelating agents, gelling agents, protein purification platforms, and therapeutic receptor-binding proteins.