A major challenge for the future is the development of effective vaccines against chronic infections and the application of therapeutic immunization to the treatment of noninfectious diseases, such as cancer, allergy and autoimmune disorders. In recent years, many of the immunological principles governing the immune response to infectious agents have been clarified and can now be exploited for the rational design of new and better vaccines. As an elucidative example, this review will describe the key immunogenic determinants of viruses and discuss how they can be harnessed for the development of tailor-made vaccines against a wide array of human diseases.