The Clean Air Regulatory Agenda (CARA) Mercury Science Program was developed to provide scientific information to support regulatory activities and accountability pertaining to atmospheric emissions of mercury in Canada. The first phase of the science program, entitled "Setting-the-Baseline'', sought to achieve the following: identify key indicators of the state-of-the-Canadian environment with respect to the transport, fate and effects of mercury; define these indicators; and, understand the processes that relate these indicators to anthropogenic emissions of mercury. To achieve these outcomes, a consultative process was used to identify the scientific needs of the agenda for mercury; understand Canada's scientific capacity; and, develop a plan to fulfill these scientific needs. The science plan that emerged from this process was structured around the themes of atmospheric monitoring, landscape-based risk assessment, ecological risk assessment, ecosystem modeling, and trends. Implementation of the science plan necessitated a multi-disciplinary and extensively partnered program. To date, the CARA Mercury Science Program is producing coordinated science at the national-scale that aims to directly assess the effectiveness of the CARA for mercury and for many of Canada's other mercury-related policies.