Research on environmental change has often focused on changes in population as a significant driver of unsustainability and environmental degradation. Demographic pessimism and limited engagement with demographic realities underpin many arguments concerning limits to growth, environmental refugees, and environment-related conflicts. Re-engagement between demographic and environmental sciences has led to greater understanding of the interactions between the size, composition, and distribution of populations and exposure to environmental risks and contributions to environmental burdens. We review the results of this renewed and far more nuanced research frontier, focusing in particular on the way demographic trends affect exposure, sensitivity, and adaptation to environmental change. New research has explained how migration systems interact with environmental challenges in individual decisions and in globally aggregate flows. Here we integrate analysis on demographic and environmental risks that often share a root cause in limited social freedoms and opportunities. We argue for a capabilities approach to promoting sustainable solutions for a more mobile world.