Nothing inherent in the discipline steers planners either toward environmental protection or toward economic development - or toward a third goal of planning: social equity. Instead, planners work within the tension generated among these 3 fundamental aims, which is called the planner's triangle, with sustainable development at the center. This center cannot be reached directly, but only approximately and indirectly, through a sustained period of confronting and resolving the triangle's conflicts. To do so, planners have to redefine sustainability, since its current formulation romanticizes the sustainable past and is too vaguely holistic. Planners would benefit from integrating social theory with environmental thinking and from combining their substantive skills with techniques for community conflict resolution, to confront economic and environmental justice.