Large-scale development projects have received significant attention in the natural and social sciences, as mines, canals, dams, pipelines, and highways shape landscapes and societies. Yet many large-scale development projects are proposed but not actually built. To the extent that such projects are studied, it is often to understand the potential socio-environmental changes they could cause, if completed. However, the impacts of unimplemented projects are not solely relegated to the future. Drawing from cases in the Americas, this Foundation will bring together an interdisciplinary group to collectively examine the socio-environmental consequences of large-scale development that hasn’t happened. Landscapes and societies are not only shaped by completed projects, but also by numerous cases of unimplemented development.