This brief is intended to bring togetherin one place, for the attention of management and the Board,the evaluation evidence on World Bank Group (WBG)cooperation. It uses the evidence developed in pastIndependent Evaluation Group (IEG) evaluations to examineWBG cooperation and the difference it makes to WBGeffectiveness, a theme of increasing importance in thecontext of the one Bank initiative. It looks at two aspectsof cooperation coordination in the programming andsequencing of WBG- supported activities and collaboration insupporting the implementation of specific interventions. WBGPresident Robert Zoellick has launched the One World Bankinitiative, designed to draw on the full range of WBGproducts, services, intellectual capital, and synergies inpursuing its mission. As possible input into theimplementation of this initiative, this brief considersexamples, insights, and lessons from IEG evaluations,focusing on WBG cooperation and its contributions and scopefor improvements. The brief itself is not an evaluation butuses evidence from past IEG evaluations to examine suchcooperation and value added for WBG effectiveness a theme ofincreasing importance.