This article analyses the role played by the European Union (EU) in the changing development architecture, focusing on the negotiation and conclusion of four high-level forums on aid effectiveness, held in Rome (2003), Paris (2005), Accra (2008) and Busan (2011). Drawing on published and unpublished material and 32 interviews with senior officials involved in these international negotiations, it reaches two main conclusions. First, EU internal effectiveness does not always translate into EU external effectiveness: it some cases, in fact, it may even be counterproductive. Second, to explain the EU’s ability to have an impact in multilateral negotiations, it is necessary to take into account the quality of the message (i.e. level of EU ambitions vis-à-vis other negotiators) and the quality of the messenger (i.e. degree of EU credibility, again in relation to other negotiators)