Though metropolitan Portland, Oregon, has perhaps the best-known growth management program in the world, one of the most important elements of that system has been conspicuously overlooked: the regional land information system (RLIS). Since RLIS was developed in the late 1980s, it has played a critical role in the development of every significant plan, the evaluation of every key policy, and the formulation of every major development model. RLIS created conditions that enabled a sophisticated and now muchstudied approach to metropolitan growth management to emerge. In this paper, we discuss the development, use, and maintenance of RLIS, illustrating its importance for both the practice of regional planning and the advancement of planning research. We begin with an overview of planning at Metro, since it is that context that provides RLIS with much of its local and political meaning. We then examine the relationship of RLIS to specific Metro planning activities. We conclude that RLIS in particular, and regional GIS systems in general, have become vital to the success of urban growth management.