The European Union (EU) consists of 27 member states. Each member state is party to the founding treaties of the union and thereby shares in the privileges and obligations of membership. Unlike members of other international organisations, the member states of the EU have agreed by treaty to shared sovereignty through the institutions of the European Union in some (but by no means all) aspects of government. Member states must agree unanimously for the EU to adopt some policies; for others, collective decision making is by qualified majority voting. Subsidiarity, meaning that decisions are taken collectively if and only if they cannot realistically be taken individually, is a founding principle of the EU.