This working paper is one of a series the EPAT/MUCIA Population and Environmental and Natural Resources team is producing. It examines major ways of thinking about the population-environment relationship over the past two centuries. The paper begins with Malthus and reviews developments to the present. Then it examines in detail six current frameworks or models for analyzing population-environment relationships. The six models include Bongaarts', Clark's, and Harrison's attempts to identify the relative impact of population growth on a limited number of forms of environmental degradation. It also examines the more complex Meadows, Meadows, and Randers WORLD3 dynamic model of the global system and International Institute of Applied Systems Analysis (IIASA) population-environment model now being applied to Mauritius. A basic finding of these models is that population growth can have a major impact on the environment. However, the impact is never simple and direct, and human organization always moderates its effect. Further, we cannot expect that slowing population growth will alleviate environmental pressures in the near term. Finally, achieving sustainable development will require a combined attack on population growth, consumption, and a variety of other human patterns of production.