The centrality of the sustainability principle to the international agendas on environment and development raises serious research problems and opportunities. The problems are manifested in such societal objectives as 'sustainable development' and a history of human-environment relationships, suggesting that the objective constitutes a paradox. The opportunities follow from the fusion of sustainable development and global environmental change research fostered by the principle. This fusion is particularly pronounced in the study of land-use/cover change in the tropical world, a subject elevated to the forefront of the research and practitioner communities. The international agendas addressing this change, such as the IGBP-IHDP core project on Land-Use/Cover Change, promise long-term, sustained research activities that join the natural and human sciences with the research and practitioner communities. They do so, however, by requiring a scale and type of interdisciplinary and inter-perspective cooperation and coordination not typical of all human sciences, including geography. The divisive character of competing approaches and explanations of land-use/cover change illustrate this situation.