International cooperation is not traditionally considered a threat to state sovereignty. It has been frequently argued that the ability to establish and maintain international relations is the very expression of sovereign status (Wæver 1995: 420). This is even the case where post-state institutions have been established, charged with formulating and executing policy decisions (Lake 2007). However, the process of European integration overseen by the institutions of the European Union (EU) as a form of international cooperation presents a challenge to conventional understandings of the continuing sovereignty of its constituent member states. This is due, it is argued, to two particular features of European integration which distinguish EU membership from more traditional forms of international cooperation: constitutionalism and majority decision-making.