This article argues that, by acting autonomously and cohesively, the European Union (EU) was able to shape the global agenda on foreign aid throughout the 2000s, particularly on the issue of donor complementarity and division of labour. By contrast, its ability to promote aid effectiveness in Sub-Saharan Africa was significantly constrained by national aid bureaucracies and by the complex aid architecture. More generally, to fully understand whether or not the EU is an effective actor, it is necessary to take into account how EU actorness contributes to the issue being discussed. At headquarter level, the European Commission sought to enhance EU actorness, which was seen as key to aid effectiveness. On the ground, national aid bureaucracies resisted EU actorness in the name of aid effectiveness.