The changing nature of economic, political and legal relationships in the world has an immense impact on the way international organizations work. The European Union (EU) and the United Nations Educational, Scientific and Cultural Organization (UNESCO) are both examples of this, yet in very different ways. The post-Second World War period provides the essential backdrop to their founding, as well as to their relationship. Like the EU, UNESCO was a postwar effort to foster international dialogue, and represented an international system moving from coexistence to cooperation. While bodies such as the League of Nations were intended to initiate formal cooperation across borders, it was not until after the Second World War that sector specific international organizations were established. The chapter explores the EU’s transition from being an observer at UNESCO to becoming a full participant on an ad hoc basis, when it so requires.