International initiatives have set ambitious goals for tree-cover expansion (TCE) to mitigate climate change and help achieve other sustainable development goals. Global mapping studies estimate that an additional billion or more hectares of the Earth’s surface can biophysically support tree cover. Yet, the feasibility of TCE depends on not only biophysical factors but also socioeconomic ones. Our pursuit aims to provide actionable information for organizations involved in TCE programs by advancing knowledge on the impacts of socioeconomic factors and their interactions with biophysical factors. Through a synthesis of spatial datasets from ecology, demography, and economics, we will map and evaluate the feasibility of TCE and its socio-environmental impacts in two years—2020 and 2030. We will advance knowledge on three important fronts: (1) the prospects for TCE on marginal agricultural land; (2) the temporal dimension of TCE mapping, by studying two important dynamic processes (the relationships among rural outmigration, marginal land, and TCE; and the interplay between tree growth rates and landholders’ time preference rates); and (3) the creation of updated and improved spatial datasets on several critical variables, including the current extent of marginal land and the cost of using it for TCE. We will focus on low- and middle-income countries, where most of the estimated additional global area for TCE is located and the factors we will examine are especially relevant. A group of senior practitioner-experts will advise us during the pursuit to ensure the practical value of our work.