The Canadian Mercury Science Assessment is the first comprehensive scientific evaluation and synthesis of mercury (Hg) in the Canadian environment. The assessment is the outcome of a partnership between the Clean Air Regulatory Agenda (CARA) Mercury Science Program, led by Environment Canada, and the Canadian Arctic Northern Contaminants Program (NCP), led by Aboriginal Affairs and Northern Development Canada. The CARA Mercury Science Program was developed in 2007 to establish the scientific knowledge base to support regulatory decision-making for Hg. The intention of the program was to (1) determine key indicators of the effects of atmospheric emissions of Hg on environmental quality and human health; (2) measure current and past levels of these indicators; and (3) develop the capacity to predict changes in these indicators associated with changes in levels of atmospheric emissions of Hg or in the receiving environment (Morrison, 2011). The geographic focus of the CARA Mercury Science Program was south of the Arctic Circle. The NCP was established in 1991 in response to concerns about human exposure to elevated levels of contaminants, such as Hg, in fish and wildlife species that are important to the traditional diets of northern aboriginal people. Since its beginning, this program has supported significant research on the transport, transformation, and fate of Hg in Canadian Arctic ecosystems (NCP, 2012). The geographic focus of the NCP program is north of the Arctic Circle, and the program is complementary to the CARA Mercury Science Program. Monitoring and research in support of these 2 programs provide the foundation of this assessment, a foundation augmented by science supported by other Environment Canada programs, Health Canada, Natural Resources Canada, Fisheries and Oceans Canada, provincial and territorial governments, the Natural Sciences and Engineering Research Council, International Polar Year, and industry.