This chapter focuses on some of the challenges posed by regionalized water resources decision making and some of the methods and techniques that are being applied to meet at least part of these challenges. It discusses three case studies: watershed-based regionalization at the Tennessee Valley Authority; regionalization as a legal function: water rights on the Upper South Platte River; and a legal regionalization: Colorado River management. The formal nature of water resources decision making also manifests itself in its administrative structures. One might be tempted to suggest that prior appropriation can be a rather wasteful way of managing a river basin. After all, when a senior downstream user claims water, all junior upstream users have to give up diversion in order to satisfy the downstream user. The resultant South Platte Water Rights Management System became operational in 1994 and has been reasonably successful in administrating water rights in the basin.