ESTER BOSERUP HAS ARGUED THAT SOCIETIES across the world have responded to increasing land scarcity in a strikingly similar and predictable manner. These societies have moved from shifting cultivation (land-extensive) systems to sedentary (land-intensive) cultivation systems. This process of agricultural intensification is usually associated with the adoption of technologies for soil fertility maintenance, labor savings, and land investments. During the early stages of intensification these technologies, such as manure use, animal draft power, and the like, are usually farmer generated. Scienceand industry-based technical change becomes important only under higher farming intensities and where populations are growing extremely rapidly. While examples abound of the population and market demand-induced productivity growth through intensification, there are other examples where intensification has led to reduced labor productivity. Declining productivity has sometimes been accompanied by soil depletion, exhaustion, and even abandonment (National Research Council, 1986). The magnitude and severity of the problem depend on the rate of population growth, the extent of institutional rigidities, and the nature of the agroclimatic environment (climate, soil type, and slope characteristics of the region). This essay reviews and synthesizes case study evidence from Africa and Asia on the institutional and environmental constraints to successful intensification. The following are identified as the major causes of the unsuccessful transition to sustainable pennanent cultivation systems: (1) Institutional innovations, especially the evolution of long-term rights to land, although induced by population growth, often tend to occur at a slower pace. (2) Despite secure longterm tenure to land, free rider problems may prevent collective action for making watershed-level investments to prevent land degradation. (3) In marginal environments, the returns to preventive land investments may be low. And (4)