Bacterial outer membrane vesicles (OMVs) are vesicles of lipids released from the outer membranes of Gram-negative bacteria. These vesicles were the first bacterial membrane vesicles (MVs) to be discovered, while Gram-positive bacteria release vesicles as well. Outer membrane vesicles were first discovered and characterized using transmission-electron microscopy by Indian Scientist Prof. Smriti Narayan Chatterjee and J. Das in 1966-67. OMVs are ascribed the functionality to provide a manner to communicate among themselves, with other microorganisms in their environment and with the host. These vesicles are involved in trafficking bacterial cell signaling biochemicals, which may include DNA, RNA, proteins, endotoxins and allied virulence molecules. This communication happens in microbial cultures in oceans, inside animals, plants and even inside the human body. Gram-negative bacteria deploy their periplasm to secrete OMVs for trafficking bacterial biochemicals to target cells in their environment. OMVs also carry endotoxic lipopolysaccharide initiating disease process in their host. This mechanism imparts a variety of benefits like, long-distance delivery of bacterial secretory cargo with minimized hydrolytic degradation and extra-cellular dilution, also supplemented with other supportive molecules (e.g., virulence factors) to accomplish a specific job and yet, keeping a safe-distance from the defense arsenal of the targeted cells. Biochemical signals trafficked by OMVs may vary largely during 'war and peace' situations. In 'complacent' bacterial colonies, OMVs may be used to carry DNA to 'related' microbes for genetic transformations, and also translocate cell signaling molecules for quorum sensing and biofilm formation. During 'challenge' from other cell types around, OMVs may be preferred to carry degradation and subversion enzymes. Likewise, OMVs may contain more of invasion proteins at the host-pathogen interface (Fig. 1). It is expected, that environmental factors around the secretory microbes are responsible for inducing these bacteria to synthesize and secrete specifically-enriched OMVs, physiologically suiting the immediate task. Thus, bacterial OMVs, being strong immunomodulators, can be manipulated for their immunogenic contents and utilized as potent pathogen-free vaccines for immunizing humans and animals against threatening infections. Biogenesis and movement Gram-negative bacteria have a double set of bilayers. An inner bilayer, the inner cell membrane, encloses the cytoplasm or cytosol. Surrounding this inner cell membrane there is a second bilayer called the bacterial outer membrane. The compartment or space between these two membranes is called the periplasm or periplasmic space. In addition, there is a firm cell wall consisting of peptidoglycan layer, which surrounds the cell membrane and occupies the periplasmic space. The