This review presents a brief outline of our current knowledge of the structure and chemical composition of the outer membrane vesicles (OMVs), originating from the surface of Gram negative bacteria including their outer membrane proteins and lipopolysaccharides. Moreover, the functional roles and applications of OMVs in medical research such as OMV-based vaccines, OMV adjuvants properties, OMV carriers in conjugated vaccines as well as in drug vehicles and delivery systems are discussed. Finally, new applications of these macromolecules as biotechnological tools are briefly presented.