Listeria monocytogenes is a Gram-positive bacterial pathogen that can cause disease in humans and a variety of animal species. Although listeriosis is increasingly recognized as a severe disease in dairy animals, including sheep, goats and cattle, it is still regarded by some as a relatively uncommon disease, probably because it may be underreported and underdiagnosed. L. monocytogenes is of particular concern not only because it may cause significant disease and financial tolls for the dairy livestock industry, but also due to the human health significance of this organism. Human listeriosis is primarily a foodborne disease, which is estimated to be responsible for about 2500 cases in the United States and for about 1600 cases annually in the European Union. Although the number of human listeriosis cases is low as compared to many other foodborne diseases, listeriosis has a high case mortality rate of about 20%. Thus in the United States alone, there are an estimated 500 human deaths attributable to listeriosis annually. Stringent control of L. monocytogenes in farm and food-processing environments and control and prevention of listeriosis in food-producing animals are important measures to assure human and animal health.