Bacteriocins from lactic acid bacteria are ribosomally produced peptides (usually 30-60 amino acids) that display potent antimicrobial activity against certain other Gram-positive organisms. They function by disruption of the membrane of their targets, mediated in at least some cases by interaction of the peptide with a chiral receptor molecule (e.g., lipid II or sugar PTS proteins). Some bacteriocins are unmodified (except for disulfide bridges), whereas others (i.e. lantibiotics) possess extensive post-translational modifications which include multiple monosulfide (lanthionine) bridges and dehydro amino acids as well as possible keto amide residues at the N-terminus. Most known bacteriocins are biologically active as single peptides. However, there is a growing class of two peptide systems, both unmodified and lantibiotic, which are fully active only when both partners are present (usually 1:1). In some cases, neither peptide has activity by itself, whereas in others, the activity of one is enhanced by the other. This review discusses the classification, structure, production, regulation, biological activity, and potential applications of such two-peptide bacteriocins.