The construction of roads and other large-scale infrastructure projects, and the secondary impacts they precipitate, are among the key drivers of change in tropical forests. The proposed expansion of a road in the buffer zones of Peru's Manu National Park and Amarakaeri Communal Reserve, in the country's Amazon region, threatens biodiversity and indigenous communities in one of the world's most species-rich and environmentally sensitive rainforest areas. In particular, road expansion is likely to result in uncontrolled colonization, deforestation, and the illicit extraction of timber and other natural resources, as well as an increase in social conflict between resource extractors and indigenous communities. Furthermore, the development of infrastructure in the Manu region puts at risk Peru's international commitments regarding climate change by promoting, rather than avoiding, forest loss. A number of viable alternatives to further road expansion are available to achieve economic development and improved mobility in Manu, including agricultural intensification, improved land-use planning, and a less invasive transportation infrastructure. Given the growth in the global road network expected in the coming decades, as well as the common factors underlying the expansion of such infrastructure across tropical, developing countries, the issues surrounding road expansion in Manu and the compromise solutions that we propose are broadly applicable to efforts to achieve sustainable development in other remote, tropical regions.