The paper introduces a Special Feature ofWetlands concerned with the ecology and management of the Murray Darling Basin, Australia. The Murray and Darling River systems in SE Australia combine to form the largest draining basin on the continent and the most economically important. The river system supports 16 wetlands listed as internationally important under the Ramsar convention, and sustains nationally significant populations of waterbirds, and endemic flora and fauna. Many of these values have been threatened by the development of water resources, particularly in the southern tributaries, and the diversion of water for irrigated agriculture. The restoration of ecological health within the Murray Darling is contingent on the optimal use of water reserved for environmental use. This objective can only be achieved through the development and application of quantitative, testable models linking environmental water regimes to ecological outcomes. This Special Feature of Wetlands explores the use of evidence in support of environmental water management, with papers considering the standards of evidence, the testing of assumptions relating to indicator species, the formulation of empirically-based flow-response models and the incorporation of these relationships in decision support tools. The further testing and development of quantitative predictive models is advocated as a key objective of environmental flow monitoring.