CSIRO Flagship Clusters are large scale research programs with an emphasis on people and partnerships working on a collection of strongly integrated projects relevant to a Flagship's goals.  The Ecological Responses to Altered Flow Regimes Cluster was funded to address ecological knowledge gaps associated with the impacts of flow alteration due to drought and water resource development, and to help predict the responses of organisms to environmental flows.  This presentation will describe the establishment of the Cluster and its objectives, which will provide a context for the remainder of the presentations in this Special Session.