Anthropogenic activities have increased the fluxes of many trace metals into the oceans, changing their concentrations and distribution patterns. Despite their low dissolved concentrations, a number of these metals can still pose human and ecological risks. Some of these metals are well known (e.g. Pb, Hg), while others, such as the rare earth elements, represent emerging problems that impose new analytical challenges and environmental concerns. Defining the baselines of trace contaminants, identifying and quantifying the processes that control their transport, fate, and cycling are important issues to protect the ocean environment, safeguard human health, and support national and international marine decision-making.