There has been great interest in the development of extremely potent antibacterial lantibiotic peptides for medicinal use and in food preservation. Of central importance to this endeavor is a strong understanding of which parts of the peptides are required for activity and which parts are expendable. Nisin, lacticin 481, nukacin ISK-1, mersacidin, lacticin 3147 and haloduracin represent many different types of lantibiotic peptides. In recent years, considerable advances toward understanding the structure-activity relationship of each of these lantibiotic systems have been achieved. This review will focus on the individual systems and the valuable information obtained from the many mutants produced.