Fluke infections cause economic losses in production systems throughout the world. Fasciola hepatica, the most important trematode of domestic ruminants, is the most common cause of liver fluke disease in temperate areas of the world. In the US, it is endemic along the Gulf Coast, the West Coast, the northern Rocky Mountain region, and other areas of high rainfall with poorly drained or heavily irrigated pastures. It is present in eastern Canada, British Columbia, and South America and is of particular economic importance in the British Isles, western and eastern Europe, Australia, and New Zealand. Fasciola gigantica is economically important in Africa and Asia and is also found in Hawaii. Fascioloides magna has been reported in at least 21 US states and in Europe. In North America, Dicrocoelium dendriticum is confined mainly to the northeastern US and the Atlantic provinces of Canada. It was recently introduced into Alberta, Canada. It is widespread in some areas in Europe and Asia. Eurytrema spp, the pancreatic flukes, parasitize sheep, pigs, buffalo, and cattle in Brazil and parts of Asia. Several species of paramphistomes, or rumen flukes, are found throughout much of the world.