Despite decades of attention by conservationists, deforestation remains a critical problem in Latin America, particularly in agricultural frontiers like the Amazon and the lowlands of CentralAmerica. The limited impact of conservation initiatives in such regions stems partly from a poor understanding of the socioeconomic and land use dynamics that typify frontiers. Moreover, conservation organizations tend to disregard the economic and policy factors at various scales that contribute to deforestation pressures in developing countries. This article describes a study of recent socioeconomic and land use changes associated with the ongoing, rapid economic integration of Petén, Guatemala's main frontier region, and considers their implications from the standpoint of sustainable land use and forest conservation. The research relied on a range of primary and secondary data, including a comparison of survey data gathered by the author in one agriculturally important area of Petén before and after roads to the region were paved in the late 1990s, leading to tighter links with other parts of the country. The resulting economic integration of 133 Downloaded by [University of Chicago Library] at 17:45 16 November 2014 134 A. J. Shriar this once isolated region has made it more difficult for its farmers to compete with larger, more efficient producers elsewhere in Guatemala and beyond, and to survive in the face of downward pressures on farm gate prices. Most of the households in the study area have thus become poorer, their farming systems less diverse, and the concentration of land ownership and landlessness have increased. Such socioeconomic marginalization limits the ability of farmers to manage their land in a sustainable manner. It also forces a growing number of people to migrate in search of a decent livelihood, in some cases into remaining "protected" areas of forest in the Maya Biosphere Reserve.