PIP: This article reviews the nature and scale of the problems between natural resource management (NRM), agricultural productivity, and population growth in developing countries. It suggests a framework for examining the dynamics of land quality change, and reviews the evidence on land management under population pressure in tropical hillside areas and suggests some lessons learned for policy development. The evidence suggests that the effect of population on land quality is unknown; it depends upon economic and institutional factors. Aggregate data obscures the dynamics of change. There are four distinct patterns of land use changes with different market, population, and agro-environmental conditions: irrigated lands, high potential rain-fed lands, long-settled marginal lands, and frontier marginal lands. Sustainable NRM and strategies of agricultural development vary with population and market growth in these four areas. Currently 50% of the poorest people live on marginal lands. When countries and regions are more dependent upon marginal lands for food production, the key environmental issues are devegetation, nutrient depletion, and erosion. The 1997 Templeton and Scheer review examined 150 studies that focused on land use, intensity, and quality under forest, crops, and pastures in hilly-mountainous areas. Studies suggest that many hill and mountain areas could sustain high production levels without excessive resource degradation, depending upon the impact of microeconomic incentives on choice of production systems. Local populations cannot cope with the challenge of sustainable intensification without supportive policy and institutions.