Costa v ENEL in the context of "Member state of the European Union"

The European Union (EU) is a supranational union of 27 member states that are party to the EU's founding treaties, and thereby subject to the privileges and obligations of membership. They have agreed by the treaties to share their own sovereignty through the institutions of the European Union in certain aspects of government. State governments must agree unanimously in the Council for the union to adopt some policies; for others, collective decisions are made by qualified majority voting. These obligations and sharing of sovereignty (also known by some as "pooling of sovereignty") within the EU make it unique among international organisations, as it has established its own legal order which by the provisions of the founding treaties is both legally binding and supreme on all the member states (after a landmark ruling of the ECJ in 1964). A founding principle of the union is subsidiarity, meaning that decisions are taken collectively if and only if they cannot realistically be taken individually.

Each member country appoints to the European Commission a European commissioner. The commissioners do not represent their member state, but instead work collectively in the interests of all the member states within the EU.