Lantibiotics are a unique class of peptide antibiotics. Recent studies of the proteins involved in the elaborate post-translational modifications of lantibiotics have revealed that these enzymes have relaxed substrate specificity. These modifications include the dehydration of serine and threonine residues followed by the intramolecular addition of cysteine thiols to the unsaturated amino acids to create an intricate polycyclic peptide. The use of peptide engineering in vivo and in vitro has allowed investigation of their biosynthetic machinery. Several members utilize a unique mode of biological action that involves the sequestration of lipid II, a crucial intermediate in peptidoglycan biosynthesis, to form pores in bacterial membranes.