Exploiting new resource “frontiers,” such as agricultural land and mineral reserves, is a fundamental feature of economic development in poor economies. Yet frontier-based development is symptomatic of a pattern of economy-wide resource exploitation in developing economies that: (a) generates little additional economic rents, and (b) what rents are generated are not being reinvested in other sectors. Such development is inherently unsustainable. The following paper explains this phenomenon, and provides evidence that long-run expansion of agricultural land and oil and natural gas proved reserves across poor economies is associated with lower levels of real income per capita. The paper proposes a frontier expansion hypothesis to explain why the structural economic dependence of these economies on frontier land expansion and resource exploitation is not conducive to sustained long-run growth. The key to sustainable economic development in poor economies will be improving the economic integration between frontier and other sectors of the economy, targeting policies to improved resource management in frontier areas and overcoming problems of corruption and rent-seeking in resource sectors. Copyright Springer Science+Business Media, Inc. 2007Economic development, Frontier, Natural capital, Natural resources, Resource-abundant economies, Sustainable development, O13, O41, Q32, Q33,