The prevention of many infectious diseases, allergies, autoimmune diseases, and cancer continues to be a challenge in the twenty-first century. Nonetheless, considerable advances have already been made, such as the eradication of certain infectious diseases and effective control of many others, and new technology is being developed in areas related to molecular biology, recombinant DNA, protein biochemistry, microbiology, and immunology. The current trends point to continued progress in coming years. Technical skills will become highly refined, so that any antigen or epitope can be presented in a highly immunogenic form within a vaccine. Modern technology has led to the formulation of a new paradigm in vaccine development, in which the genomic and/or proteomic aspects of diseases are analyzed a priori to identify factors implicated in the immune response that may serve as promising vaccine candidates.