The EU Treaties as Constitutional Framework: TEU and TFEU
The Treaties of the European Union — the Treaty on European Union (TEU) and the Treaty on the Functioning of the European Union (TFEU) — constitute the constitutional foundation of the EU legal order. As amended most recently by the Treaty of Lisbon (2007, in force 2009), the Treaties establish the Union’s objectives, institutions, legal instruments, and competences, while also setting forth the fundamental values that underpin the European project. The Court of Justice has characterised the Treaties as a “constitutional charter” (Opinion 1/91), reflecting their fundamental character as the supreme source of EU law, superior to all secondary legislation and binding on all Member States and institutions.
The Treaty on European Union (TEU)
The TEU contains the foundational provisions of the Union. Its Title I (Common Provisions) sets out the Union’s values, objectives, and fundamental principles. Article 2 TEU establishes the values on which the Union is founded: respect for human dignity, freedom, democracy, equality, the rule of law, and respect for human rights. Article 3 TEU defines the Union’s objectives, including the promotion of peace, the Union’s values, and the well-being of its peoples; an area of freedom, security, and justice without internal frontiers; the establishment of the internal market; and sustainable development based on balanced economic growth and price stability.
Title II (Provisions on Democratic Principles) articulates the Union’s democratic foundations, including the principle of representative democracy (Article 10), participatory democracy through civil society dialogue and the European Citizens’ Initiative (Article 11), and the role of national parliaments in ensuring subsidiarity compliance (Article 12). Title III (Institutions) establishes the institutional framework: the European Parliament, the European Council, the Council, the European Commission, the Court of Justice of the European Union, and the European Central Bank. Each institution must act within the limits of the powers conferred by the Treaties.
Title V (External Action) sets out the principles and objectives of the Union’s external action, including the Common Foreign and Security Policy (CFSP). Title VI (Final Provisions) includes Article 48 on treaty amendment, Article 49 on accession of new Member States, and Article 50 on voluntary withdrawal from the Union, introduced by the Treaty of Lisbon and exercised by the United Kingdom in 2020.
The Treaty on the Functioning of the European Union (TFEU)
The TFEU is the longer and more detailed Treaty, containing the substantive provisions governing EU policies and the functioning of the internal market. It is organised in seven parts covering: principles (Part I), non-discrimination and citizenship of the Union (Part II), internal policies and actions including the internal market, competition, economic and monetary union, and area of freedom, security and justice (Part III), association of overseas countries and territories (Part IV), external action (Part V), institutional and financial provisions including detailed rules on each institution and the budgetary process (Part VI), and general and final provisions (Part VII).
The TFEU contains the detailed legal bases for EU action, specifying where the Union may act, by what procedure, and with what legal instruments. Article 114 TFEU is the primary legal basis for internal market harmonisation, enabling the adoption of measures for the approximation of national laws affecting the establishment or functioning of the internal market. Article 352 TFEU, the flexibility clause, permits the Council to adopt measures necessary to attain Treaty objectives where the Treaties have not provided the necessary powers. The TFEU also contains the competition rules (Articles 101–109), the economic and monetary union provisions (Articles 119–144), and the judicial system provisions (Articles 251–281).
Amendment Procedures
Article 48 TEU establishes two amendment procedures. The ordinary revision procedure under Article 48(2)–(5) applies to amendments to the fundamental architecture of the Treaties. A convention composed of representatives of national parliaments, governments, the European Parliament, and the Commission examines the proposed amendments and adopts recommendations by consensus. An Intergovernmental Conference (IGC) then negotiates the amendments, which enter into force after ratification by all Member States in accordance with their constitutional requirements. This procedure was used for the Treaties of Maastricht, Amsterdam, Nice, and Lisbon.
The simplified revision procedures under Article 48(6)–(7) allow amendment of Part III of the TFEU (internal policies) by unanimous decision of the European Council with the consent of the European Parliament, and permit the European Council to authorise the Council to act by qualified majority voting or under the ordinary legislative procedure in areas where the Treaties require special procedures. These simplified procedures do not require a convention or IGC but still require national parliamentary approval. Passerelle clauses enable changes to voting procedures without formal treaty amendment, and general passerelle clauses apply across specific policy areas.
Protocols and Declarations
Protocols annexed to the Treaties have the same legal value as the Treaties under Article 51 TEU. They contain detailed provisions on specific issues including the role of national parliaments, the application of subsidiarity and proportionality, the internal market and competition, the European System of Central Banks, the Court of Justice, and the location of seats of institutions. Protocols may provide for opt-outs or special arrangements for particular Member States, as with Protocols 21 and 22 concerning the UK and Ireland’s position on the Area of Freedom, Security and Justice, and Protocol 30 concerning Poland’s position on the Charter of Fundamental Rights.
Declarations annexed to the Treaties have legal significance for interpretation. Declarations by the Conference are adopted by all Member States and may be used as interpretative aids by the CJEU. Unilateral declarations by individual Member States have more limited interpretive value. Declaration No. 17 concerning primacy, annexed to the Treaty of Lisbon, recalls the existing case law of the CJEU that EU law has primacy over national law, providing political confirmation of this foundational principle.
The Constitutionalization of the EU Legal Order
The European Court of Justice has played a central role in the constitutionalization of the Treaties. Through landmark judgments including Van Gend en Loos (Case 26/62) establishing direct effect, Costa v ENEL (Case 6/64) establishing supremacy, and Les Verts v Parliament (Case 294/83) recognising the Treaties as a constitutional charter, the CJEU has transformed the Treaties from traditional international agreements into a constitutional legal order.
This constitutionalization has several dimensions. The Treaties create directly enforceable rights for individuals, not merely obligations between states. They establish a hierarchy of norms in which EU law prevails over conflicting national law. They create a complete system of legal remedies enabling individuals and institutions to challenge EU acts. They provide for judicial review of EU institutions and Member State compliance. They establish fundamental rights protection through the Charter of Fundamental Rights and general principles of EU law. The Treaties thus function as a constitution for the European Union, even though they retain the form of international treaties and depend on Member State ratification for their authority.