In recent years many peptide antibiotics have been shown to be ribosomally synthesized. Among these are many microcins, produced by diverse strains of gram-negative bacteria. While the structures and modes of action of these peptide antibiotics vary widely, many of them share several important features. Their synthesis is often induced by the cessation of growth. In addition, many of them undergo unusual posttranslational modifications to yield the mature molecule, which is often exported from the cell by a dedicated export apparatus. The genes involved in modification and export of the peptide antibiotics are generally found adjacent to the structural gene and are under the same regulation. The results supporting these conclusions are reviewed and discussed in this chapter.