There continues to be congressional interest in limiting human activity in certain areas of the marine environment, as one response to mounting evidence of declining environmental quality and populations of living resources. The purposes of proposed additional limits would be both to stem declines and to permit the rehabilitation of these environments and populations. One method of implementing this concept is for Congress to designate areas where activities would be limited, often referred to as marine protected areas (MPAs). Translating the MPA approach into a national program, however, would require that Congress resolve many economic, ecological, and social dilemmas.