Lactic acid bacteria (LAB), widely used in the food industry, are present in the intestine of most animals, including humans. The potential use of these bacteria as mucosal delivery vehicles for vaccinal, medical or technological use has been extensively investigated. Lactococcus Iactis, a LAB species, is a potential candidate for the production of biologically useful proteins and for plasmid DNA delivery to eukaryotic cells. Several delivery systems have been developed to target heterologous proteins to a specific cell location (i.e., cytoplasm, cell wall or extracellular medium) and more recently to efficiently transfer DNA to eukaryotic cells. A promising application of L lactis is its use for the development of live mucosal vaccines. Here, we have reviewed the expression of heterologous protein and the various delivery systems developed for L. lactis, as well as its use as an oral vaccine carrier. (C) 2011 Elsevier Inc. All rights reserved.