Microcins are gene-encoded antibacterial peptides, with molecular masses below 10 kDa, produced by enterobacteria. They are secreted under conditions of nutrient depletion and exert potent antibacterial activity against closely related species. Typical gene clusters encoding the microcin precursor, the self-immunity factor, the secretion proteins and frequently the post-translational modification enzymes are located either on plasmids or on the chromosome. Contrary to most of the antibiotics of microbial origin, which are synthesized by multimodular enzymes termed peptide synthetases, microcins are ribosomally-synthesized as precursors further modified enzymatically. They form a restricted class of potent antibacterial peptides. Fourteen microcins have been reported until now, among which only seven have been isolated and characterized. Despite the low number of known representatives, microcins exhibit a diversity of structures and antibacterial mechanisms. This review gives an updated overview of microcin structures, biosyntheses, antibacterial activities and mechanisms of action. It shows how fascinating, clever and complex the mechanisms used by microcins are to kill target bacteria. Covering 1982 to 2006.