Vaccination is one of the most efficient and cost effective methods of promoting human health and has been in clinical use for at least 200 years. Nevertheless, infectious diseases continue to constitute a constant threat to the well being of humanity. Common pathogens, once believed to be under control, acquire increased virulence and resistance to drugs, while exotic microorganisms emerged from hidden reservoirs to cause yet incurable diseases in humans. These changes, together with epidemic outbreaks related to political and socio-economic instabilities, increase the needs for the development of new, advanced vaccines. In this volume, devoted to the proceedings of the 39th OHOLO Conference, we present some of the recent strategies for the design and production of novel vaccines. The advent of recombinant DNA technology has stimulated the production of several subunit vaccines. In spite of the obvious advantages to this approach, the limited immuno­ genicity of many subunit candidates has hindered their development. Strategies to enhance the immunogenicity of subunit vaccines is therefore critical. Several approaches toward this goal, including design of novel adjuvants and delivery systems as well as design of advantageous carriers, are presented here. Among the carriers evaluated here are polypep­ tides (flagellin, HBV core antigen, J3-galactosidase), attenuated virions (Vaccinia, Sindbis), and nonpathogenic licensed bacteria (Salmonella).