Water resources management at the river basin scale is, under the perspective of institutional analysis, a decentralization process aiming at maximizing socio-economic benefits related to water resources and minimizing transaction costs, in both the implementation of new institutional arrangements and the adaptation of existent arrangements to changing situations. After describing the two key-principles of decentralization and participation, the current work analyzes a number of important characteristics, factors and variables influencing the successful implementation of river basin management decentralization processes. The intent of this paper is to provide a practical tool for researchers and policy-makers, useful to describe - on a case-by-case basis - the performance of water resources management institutional arrangements at the river basin level.