This is a worldwide guide for the identification of marine mammals and those cetaceans, seals, and sirenians also found in freshwater. The 119 species include a variety of taxa: baleen whales, toothed whales, dolphins, porpoises, seals, sea lions, sirenians, marine otters, and the polar bear. There is an introduction with notes on marine mammal distribution in regard to oceanography and marine mammal identification, a glossary of technical terms, illustrated keys to species, illustrated family keys for skulls, species sheets, and a table of species by major marine fishing areas. Every species sheet includes scientific and official FAO names, diagnostic features, notes on similar species, size, distribution, biology, habitat, behaviour, exploitation, and IUCN (World Conservation Union, formerly International Union for the Conservation of Nature and Natural Resources) status. The work is fully indexed and includes a list of referentes and sources for further reading.