European Union law in the context of "Primacy of European Union law"

The European Union (EU) is a supranational political and economic union of 27 member states that are located primarily in Europe. The Union has a total area of 4,233,255 km (1,634,469 sq mi) and an estimated population of more than 450 million as of 2025. The EU is often described as a sui generis political entity combining characteristics of both a federation and a confederation.

Containing 5.5% of the world population in 2023, EU member states generated a nominal gross domestic product (GDP) of around €17.935 trillion in 2024, accounting for approximately one sixth of global economic output. Its cornerstone, the Customs Union, paved the way to establishing an internal single market based on standardised legal framework and legislation that applies in all member states in those matters, and only those matters, where the states have agreed to act as one. EU policies aim to ensure the free movement of people, goods, services and capital within the internal market; enact legislation in justice and home affairs; and maintain common policies on trade, agriculture, fisheries, and regional development.

The institutions of the European Union are the seven principal decision-making bodies of the European Union and Euratom governed under the Treaties of the European Union and European Union law. They are, as listed in Article 13 of the Treaty on the European Union:

• the European Parliament,
• the European Council (of heads of state or government),
• the Council of the European Union (of member state ministers, a council for each area of responsibility),
• the European Commission,
• the Court of Justice of the European Union,
• the European Central Bank and
• the European Court of Auditors.

Institutions are distinct from both advisory bodies to the European Union and agencies of the European Union.

The European Court of Justice (abbr. ECJ), officially the Court of Justice (French: Cour de Justice), is the supreme court of the European Union (EU) in matters of European Union law. As a part of the Court of Justice of the European Union, it is tasked with interpreting EU law and ensuring its uniform application across all EU member states under Article 263 of the Treaty of the Functioning of the European Union (TFEU).

The Court was established in 1952, and is based in Luxembourg. It is composed of one judge per Member State – currently 27 – although it normally hears cases in panels of three, five or fifteen judges. The Court has been led by president Koen Lenaerts since 2015.

Flaminio Costa v ENEL (1964) Case 6/64 was a landmark decision of the European Court of Justice which established the primacy of European Union law (then Community law) over the laws of its member states.

Switzerland is not a member state of the European Union (EU). It is associated with the Union through a series of bilateral treaties in which Switzerland has adopted various provisions of European Union law in order to participate in the Union's single market, without joining as a member state. Among Switzerland's neighbouring countries, all but one (the microstate Liechtenstein) are EU member states.

The Court of Justice of the European Union (CJEU) (French: Cour de justice de l'Union européenne or "CJUE"; Latin: Curia) is the judicial branch of the European Union (EU). Seated in the Kirchberg quarter of Luxembourg City, Luxembourg, this EU institution consists of two separate courts: the Court of Justice and the General Court. From 2005 to 2016, it also contained the Civil Service Tribunal. It has a sui generis court system, meaning 'of its own kind', and is a supranational institution.

The CJEU is the chief judicial authority of the EU and oversees the uniform application and interpretation of European Union law, in co-operation with the national judiciary of the EU member states. CJEU also resolves legal disputes between national governments and EU institutions, and may take action against EU institutions on behalf of individuals, companies, or organisations whose rights have been infringed.

In general, the law of the European Union is valid in all of the twenty-seven European Union member states. However, occasionally member states negotiate certain opt-outs from legislation or treaties of the European Union, meaning they do not have to participate in certain policy areas. Currently, three states have such opt-outs: Denmark (two opt-outs), Ireland (two opt-outs) and Poland (one opt-out). The United Kingdom had four opt-outs before leaving the Union.

This is distinct from the enhanced cooperation, a measure introduced in the Treaty of Amsterdam, whereby a minimum of nine member states are allowed to co-operate within the structure of the European Union without involving other member states, after the European Commission and a qualified majority have approved the measure. It is further distinct from the Mechanism for Cooperation and Verification, whose lifting is conditional on the relevant member states meeting certain benchmarks, and temporary derogations from certain areas of cooperation (such as the Schengen Agreement and the eurozone) until the relevant member states satisfy the entry conditions.