Humans have hunted all for centuries, sometimes to the point of near extinction of selected species. Recovery of exploited populations is proceeding under the guidance of various international commissions and regulatory groups. There has been a major surge in the literature on trace metal composition of marine mammals during the past 30 years. Mammals include the whales, porpoises, seals, dolphins, walruses, sea otters, and their relatives. The majority of the cetaceans and pinnipeds are exclusively marine, some frequenting the coast, but others oceanic, seldom approaching land. Many undertake extensive migrations and are widely distributed. A significant portion of the variability in trace metal concentrations within and between species of marine mammals is attributed to geographic location, year of capture, season, gender, blubber thickness, age, and fatty acid content. Tables have been outlined that illustrate concentrations of various trace metals in field collections of mammals. Some of the associated functions and defects due to the presence or absence of these trace metals have also been subsequently highlighted.