Atlantic halibut and Pacific halibut off the Atlantic and Pacific coasts of North America share many biological characteristics. The conventional separation of the halibut into separate species is not uniformly accepted. Reproduction and early life history are nearly identical, although the extensive drift of Pacific halibut eggs and larvae and countermigration as juveniles have not been demonstrated for the Atlantic halibut. Adult halibut undergo migration from winter spawning grounds along the upper continental slope to summer feeding grounds on the continental shelf. The two halibuts show the same pattern of age and growth. They exhibit different trophic selectivity, as small Atlantic halibut consume a higher proportion of invertebrates as samll fish and large Atlantic halibut consume a higher proportion of fish, compared to Pacific halibut. Halibut management in the Atlantic and Pacific varies dramatically. Atlantic halibut in Canada were managed with other groundfish until 1988 and are not managed in the United States. Pacific halibut have been managed by an international commission under treaty between the United States and Canada since 1923. Atlantic halibut have produced from 1000 to 5000 t annually, mainly off Canada, while Pacific halibut have produced 12,000 to 45,000 t, mainly off Alaska. Biological and fishery data are collected more extensively for the Pacific halibut, for which detailed stock assessment is conducted.