This report aims to clarify the requirements of sustainable energy development. It begins by describing and contextualizing current patterns of global energy use, production, and resources. It then presents a global long-range Conventional Development Scenario for energy to the year 2050 assuming mid-range population and economic projections, gradual evolution of human and natural systems, and global convergence of technological, institutional, and cultural processes. The report identifies potential environmental, resource, and social stresses related to the conventional development path and explores the implications and limitations of such a path.