The Evolution of the European Treaties: From Paris and Rome to Maastricht, Amsterdam, Nice, and Lisbon

The Evolution of the European Treaties: From Paris and Rome to Maastricht, Amsterdam, Nice, and Lisbon

Introduction

The European Union did not emerge from a single constitutional act. Its legal and institutional structure developed through a succession of international treaties, each responding to a particular historical challenge and reshaping the relationship between European states, common institutions, and individuals.

The treaties are more than records of diplomatic agreements. They form the constitutional foundation of the European Union: they establish its institutions, define the limits of its authority, determine how European legislation is adopted, and regulate the relationship between EU law and the legal systems of the Member States. They also reveal the distinctive character of European integration. The Union was not created through the replacement of national constitutions by a single federal constitution. Instead, its authority developed incrementally through treaties concluded and ratified by sovereign states, while the institutions established under those treaties acquired powers that distinguish the EU from an ordinary international organisation.

The journey began with the Treaty of Paris in 1951 and the Treaties of Rome in 1957. It continued through institutional consolidation, budgetary reform, the Single European Act, and the major constitutional transformation brought about by the Maastricht Treaty. Amsterdam and Nice subsequently prepared the Union for a wider range of responsibilities and a much larger membership. The unsuccessful Constitutional Treaty of 2004 exposed the political and constitutional limits of treaty reform, while the Treaty of Lisbon eventually reorganised the legal framework and established much of the institutional structure that governs the Union today.

Understanding this evolution is essential to understanding EU law. Many features that appear straightforward in the present system—EU citizenship, the ordinary legislative procedure, qualified majority voting, the European Parliament’s legislative authority, the legal personality of the Union, and the Charter of Fundamental Rights—are the result of successive treaty reforms rather than elements of one original constitutional design.

This article examines those reforms chronologically and constitutionally, explaining not only what each treaty changed, but also why the changes mattered.

1. The Treaty of Paris: The First Constitutional Foundation (1951)

The Treaty of Paris, signed on 18 April 1951 and entering into force on 23 July 1952, established the European Coal and Steel Community (ECSC). It was the first treaty to create a European organisation with genuinely supranational powers over a defined economic sector.

Its importance lay not merely in the decision to cooperate over coal and steel. These industries were essential to industrial production and military capacity. By placing them under a common institutional framework, the six founding states—Belgium, France, the Federal Republic of Germany, Italy, Luxembourg and the Netherlands—accepted that certain decisions would no longer be made exclusively through separate national authorities.

The treaty created a distinctive institutional arrangement. The High Authority exercised executive and regulatory functions independently of national governments; the Council of Ministers represented the Member States; the Common Assembly provided a parliamentary dimension; and the Court of Justice was responsible for ensuring that the law was observed. This arrangement established an early model for the institutional balance that would later characterise the European Communities and the EU.

The Treaty of Paris also introduced an important legal principle: cooperation could involve the exercise of authority by common institutions rather than merely the coordination of national policies. The ECSC was therefore an early experiment in supranational governance.

The treaty was concluded for a period of 50 years and expired on 23 July 2002. Its expiry did not end European integration. The ECSC’s remaining assets and associated financial arrangements were dealt with within the wider European framework, while the institutional and legal experience developed under the treaty had already influenced the later Communities.

The Treaty of Paris is consequently best understood as the starting point of a constitutional process. It did not establish the European Union, but it demonstrated that European states could create common institutions capable of exercising legally defined powers beyond the traditional framework of intergovernmental cooperation. EUR-Lex+1

2. The Treaties of Rome: From Sectoral Cooperation to a Common Market (1957)

The next major development occurred with the signing of the Treaties of Rome on 25 March 1957. They established two new Communities:

• The European Economic Community (EEC).
• The European Atomic Energy Community (Euratom).

Both treaties entered into force on 1 January 1958. Their adoption marked a significant expansion of the original integration project. Whereas the ECSC concentrated on two strategic industrial sectors, the EEC sought to develop a common market across a much wider range of economic activities.

2.1 The EEC Treaty

The Treaty establishing the European Economic Community aimed to create a common market through the gradual removal of barriers between Member States. Its central economic objective was to facilitate the movement of goods, persons, services and capital.

The treaty established a framework for:

• The progressive elimination of customs duties and quantitative restrictions between Member States.
• The establishment of a common external customs tariff.
• The development of common policies, including agriculture and transport.
• The removal of restrictions affecting the movement of persons, services and capital.
• The approximation of national laws where necessary for the functioning of the common market.
• The creation of common institutions capable of developing and implementing Community policies.

The EEC Treaty was constitutionally significant because it established a general economic framework rather than a limited sectoral arrangement. It also provided the legal foundation for the development of a body of Community law that would increasingly regulate relations between states, businesses and individuals.

The common market was not intended to be achieved immediately. The treaty provided for a transitional period during which Member States would progressively fulfil their obligations. This gradual approach reflected the practical difficulty of integrating national economies with different regulatory systems, economic structures and political priorities.

2.2 The Euratom Treaty

The second Treaty of Rome established the European Atomic Energy Community. Euratom was designed to coordinate the development of nuclear energy for peaceful purposes, encourage research, facilitate investment and establish common safeguards.

Its subject matter was narrower than that of the EEC, but it created a distinct legal framework that continues to exist. Euratom was not abolished when the European Community became the European Union. It retains its own treaty and legal personality, although it shares institutions with the EU.

2.3 Common institutions and the development of Community law

The Treaties of Rome also advanced the institutional model established by the ECSC. The Commission, Council, Parliamentary Assembly and Court of Justice became central to the operation of the Communities.

The Convention on Certain Institutions Common to the European Communities, signed in 1957, provided for a common Parliamentary Assembly and a common Court of Justice. The executive structures and Councils, however, remained separate until the Merger Treaty.

The Treaties of Rome therefore established the foundations of a broader legal and institutional system. They transformed European integration from cooperation in selected industries into a project concerned with the organisation of a common economic space. European Union+2

3. The Merger Treaty: Institutional Consolidation (1965–1967)

By the middle of the 1960s, three European Communities existed: the ECSC, the EEC and Euratom. Although they shared certain institutions, each had its own executive structure and Council.

The resulting administrative complexity made institutional consolidation increasingly attractive. The Treaty establishing a Single Council and a Single Commission of the European Communities, commonly known as the Merger Treaty or Brussels Treaty, was signed on 8 April 1965 and entered into force on 1 July 1967.

It established:

• A single Commission serving the three Communities.
• A single Council replacing the separate Councils and the ECSC Special Council of Ministers.
• A unified administrative structure for the Communities.

An important distinction must be maintained. The Merger Treaty did not create one new Community or abolish the separate legal personalities of the ECSC, EEC and Euratom. Nor did it create the common Parliamentary Assembly and Court of Justice: those institutions had already been shared under the 1957 Convention.

The treaty was principally an institutional reform. It simplified the administration of European integration and made the Communities easier to operate as a coordinated system.

Its longer-term significance was that it encouraged the perception of the three Communities as parts of a broader European institutional structure, even though their legal foundations remained distinct. europarl.europa.eu+1

4. The Budgetary Treaties: Financial Independence and Parliamentary Accountability (1970 and 1975)

Treaty reform did not concern institutional organisation alone. The Communities also needed a stable financial system and clearer procedures for approving and supervising expenditure.

Two important treaties addressed these questions.

4.1 The Treaty of Luxembourg (1970)

The Treaty amending Certain Budgetary Provisions, signed in Luxembourg on 22 April 1970, introduced a system of own resources for the European Communities.

Previously, the Communities relied substantially on financial contributions from Member States. The own-resources system was intended to provide a more autonomous basis for financing Community expenditure.

The system developed through successive decisions and reforms. It included traditional own resources, such as customs duties, as well as resources calculated by reference to harmonised VAT bases and, subsequently, Member States’ gross national income.

The treaty also increased the European Parliament’s role in the budgetary process, although its powers remained limited in comparison with those of the Council.

4.2 The Treaty of Brussels (1975)

The Treaty amending Certain Financial Provisions, signed on 22 July 1975, further developed the Communities’ financial arrangements.

It strengthened Parliament’s budgetary authority and established the Court of Auditors as an independent institution responsible for examining the legality and regularity of revenue and expenditure and assessing the sound financial management of Community funds.

The Court of Auditors began operating in 1977. Its establishment was important because the expansion of common policies and expenditure required an independent mechanism of financial scrutiny.

The budgetary reforms contributed to a gradual constitutional development: the Communities were acquiring not only legislative and administrative capacities but also a more structured financial system subject to institutional oversight.

Parliament’s growing involvement in the budget also strengthened its position as a representative institution. The evolution of its budgetary powers formed part of the wider process through which it became an increasingly influential participant in European law-making. europarl.europa.eu+1

5. The Single European Act: The Legal Foundations of the Internal Market (1986–1987)

The next major reform was the Single European Act (SEA), signed in February 1986 and entering into force on 1 July 1987. It was the first substantial revision of the Treaties of Rome and represented a renewed commitment to economic integration after a period in which the development of the common market had encountered significant obstacles.

By the 1980s, the removal of customs duties had not been sufficient to establish a genuinely integrated market. National technical standards, divergent product requirements, administrative formalities, restrictions on services and other regulatory barriers continued to impede cross-border economic activity. The objective therefore shifted from creating a customs union towards completing an internal market in which economic operators could function across national borders under a more coherent legal framework.

5.1 The internal market objective

The Single European Act established the objective of completing an internal market by 31 December 1992. The internal market was conceived as an area without internal frontiers in which the free movement of goods, persons, services and capital would be ensured in accordance with the Treaties.

This objective required more than removing tariffs. It involved addressing the regulatory and administrative barriers that could prevent goods and services from circulating freely even when no customs duties applied.

The Act therefore supported a substantial programme of legislative harmonisation and regulatory approximation. It gave the Community a stronger legal basis for adopting measures designed to establish and operate the internal market.

The importance of this reform was structural. It transformed the common market from a general economic aspiration into a more specific programme of legislative action.

5.2 Qualified majority voting

One of the most consequential institutional reforms was the expansion of qualified majority voting in the Council.

Under a system requiring unanimity, each Member State could prevent the adoption of a measure by withholding its agreement. This preserved national control but could also make legislative progress difficult, particularly where a policy required the harmonisation of numerous national rules.

The Single European Act expanded qualified majority voting in several areas connected with the internal market. This enabled the Council to adopt more measures without requiring every government to agree individually.

Qualified majority voting did not eliminate unanimity from the Community system. Sensitive areas continued to require it. Nevertheless, the reform altered the balance between national veto powers and collective decision-making.

It also illustrated an important characteristic of European integration: the transfer or exercise of common authority was accompanied by institutional procedures designed to make that authority operational.

5.3 The European Parliament’s growing role

The Single European Act introduced the cooperation procedure, which gave the European Parliament a more substantial role in the legislative process.

Under the earlier consultation model, Parliament was generally asked to express an opinion, but the Council retained the decisive legislative authority. The cooperation procedure created additional stages in which Parliament could influence the content of legislation.

The Act also introduced the assent procedure in certain important areas, including accession agreements and association agreements. Under this procedure, Parliament’s approval was required, although it did not have the same power to amend the agreement as it would have under an ordinary legislative process.

These reforms did not yet establish Parliament as an equal co-legislator with the Council. They nevertheless marked a significant movement away from a system dominated by national governments.

5.4 European political cooperation

The Single European Act also gave treaty recognition to European Political Cooperation, through which Member States coordinated aspects of their foreign policies.

This was not yet the Common Foreign and Security Policy established by Maastricht. It was a more limited system of intergovernmental coordination. Its inclusion nevertheless demonstrated that European integration was beginning to extend beyond economic questions.

The Act also formally recognised the European Council in the treaty framework. The European Council, consisting of the heads of state or government and the President of the Commission, had already become an important political forum. Its formal recognition gave greater visibility to its role in providing political direction.

The Single European Act was therefore a turning point. It strengthened the Community’s capacity to legislate, expanded majority voting, increased Parliament’s influence and created a more developed legal framework for the internal market. Consilium+2

6. The Maastricht Treaty: The Creation of the European Union (1992–1993)

The Treaty on European Union, commonly known as the Maastricht Treaty, was signed on 7 February 1992 and entered into force on 1 November 1993. It represented one of the most significant constitutional developments in the history of European integration.

Until Maastricht, the European Communities had principally been concerned with economic integration, although their activities had already expanded into other fields. Maastricht created the European Union as a broader political and legal framework and introduced new forms of cooperation in foreign policy, security, justice and home affairs.

It did not simply rename the European Economic Community. It established a more complex structure in which the existing Communities formed one part of a wider Union.

6.1 The creation of the European Union and the three-pillar structure

The Maastricht Treaty established the European Union through a structure commonly described as the three-pillar system.

The first pillar consisted of the European Communities. It retained the supranational characteristics of Community law, including the central roles of the Commission, Council, Parliament and Court of Justice.

The second pillar was the Common Foreign and Security Policy (CFSP). This created a framework for cooperation between Member States on foreign policy and security matters. Its structure was predominantly intergovernmental, reflecting the sensitivity of national sovereignty in these fields.

The third pillar initially concerned cooperation in Justice and Home Affairs (JHA). It addressed matters such as immigration, asylum, external border controls, judicial cooperation and aspects of law enforcement. At this stage, it also operated mainly through intergovernmental arrangements.

The three pillars were part of one Union, but they did not operate under identical legal rules. The distinction was important because the supranational procedures and judicial mechanisms characteristic of the Community pillar did not apply in the same way to the other two pillars.

The system reflected a compromise. Member States were willing to deepen integration, but they were not prepared to subject every new area of cooperation to the same institutional and judicial arrangements.

6.2 European Union citizenship

Maastricht introduced the concept of citizenship of the European Union.

EU citizenship was linked to nationality of a Member State: every person holding the nationality of a Member State was a citizen of the Union. It did not replace national citizenship, nor did it create an independent nationality that could be acquired separately from Member State nationality.

The treaty nevertheless established a new legal relationship between individuals and the Union.

Among the rights associated with EU citizenship were:

• The right to move and reside freely within the territory of the Member States, subject to the conditions laid down in the Treaties and secondary legislation.
• The right to vote and stand as a candidate in municipal elections in the Member State of residence under the conditions applicable to its nationals.
• The right to vote and stand as a candidate in elections to the European Parliament in the Member State of residence.
• The right to diplomatic and consular protection by another Member State in a third country where the citizen’s own Member State is not represented.
• The right to petition the European Parliament and apply to the European Ombudsman.

The significance of citizenship was constitutional as well as practical. European integration was no longer framed exclusively as cooperation between states and economic operators. Individuals acquired a formally recognised status within the developing Union.

6.3 Economic and Monetary Union

The Maastricht Treaty established the legal and institutional framework for Economic and Monetary Union (EMU), including the pathway towards a single currency.

The treaty provided for a staged process involving economic convergence, coordination of monetary policies and the development of institutions responsible for monetary union. It established convergence criteria relating to price stability, government finances, exchange-rate stability and long-term interest rates.

The process eventually led to the introduction of the euro as a currency in 1999 for participating Member States, initially for accounting and electronic transactions, followed by euro banknotes and coins in 2002.

The treaty also laid the foundations for the European Central Bank and the European System of Central Banks. The ECB would become responsible for monetary policy in the euro area, subject to the objectives and institutional framework established by the Treaties.

Maastricht therefore moved European integration into an area traditionally associated with core state functions: monetary authority.

6.4 The co-decision procedure

The Maastricht Treaty introduced the co-decision procedure, which gave the European Parliament a more substantial role in adopting Community legislation.

Unlike consultation, co-decision required the Council and Parliament to reach agreement on legislation within the procedure’s scope. Parliament could therefore become a genuine participant in the legislative process rather than merely an institution asked to provide an opinion.

The procedure was initially limited to specified policy areas. Its scope was expanded by subsequent treaty reforms and it eventually became the ordinary legislative procedure under the Lisbon Treaty.

The development of co-decision was central to the gradual strengthening of democratic representation at EU level.

6.5 Subsidiarity

Maastricht also gave treaty expression to the principle of subsidiarity in areas that did not fall within the Community’s exclusive competence.

The principle required the Community to act only where the objectives of a proposed action could not be sufficiently achieved by the Member States and could, by reason of the scale or effects of the proposed action, be better achieved at Community level.

Subsidiarity was intended to regulate the exercise of powers rather than to create new EU competences. It addressed the question of which level of governance should act when both national and European action were legally possible.

This distinction remains important. The Union does not possess a general power to legislate whenever common action appears desirable. Its authority must have a treaty basis, and the exercise of that authority is subject to principles including conferral, subsidiarity and proportionality.

6.6 The European Community and the wider political Union

Maastricht changed the name of the European Economic Community to the European Community, reflecting the broader range of its activities.

The treaty also established the Common Foreign and Security Policy and the Justice and Home Affairs framework, while leaving the European Communities as the principal supranational component of the new Union.

Its constitutional importance was therefore twofold. It created the European Union as a broader political structure, and it introduced a series of new legal relationships between the Union, its Member States and their citizens.

Maastricht transformed the nature of European integration. The project was no longer confined to constructing a common market. It now included citizenship, monetary union, foreign policy coordination and cooperation in justice and internal affairs. europarl.europa.eu+2

7. The Amsterdam Treaty: An Area of Freedom, Security and Justice (1997–1999)

The Treaty of Amsterdam was signed on 2 October 1997 and entered into force on 1 May 1999. It amended the Treaty on European Union and the Treaties establishing the European Communities.

The treaty addressed several weaknesses in the Maastricht framework. It sought to improve the Union’s capacity to act, strengthen democratic participation, develop cooperation in justice and home affairs, and prepare the institutional system for future enlargement.

7.1 The development of an Area of Freedom, Security and Justice

One of the treaty’s most important objectives was the establishment of an Area of Freedom, Security and Justice.

This concept brought together several policy fields that had previously been treated through different legal arrangements. It concerned the free movement of persons, asylum, immigration, external border controls, civil judicial cooperation and aspects of police and criminal judicial cooperation.

The treaty transferred certain matters from the intergovernmental Justice and Home Affairs pillar into the Community framework. In particular, aspects of visa policy, asylum, immigration and civil judicial cooperation became subject to more supranational procedures, although special arrangements and transitional rules applied.

Police and criminal judicial cooperation largely remained within the intergovernmental third pillar at that stage.

The reform was important because it recognised that the internal market and free movement of persons required cooperation in areas such as border management, asylum and judicial assistance. The removal of internal barriers could not be separated entirely from the legal and administrative arrangements governing security and justice.

7.2 Incorporation of the Schengen acquis

The Amsterdam Treaty incorporated the Schengen acquis into the framework of the European Union through a protocol.

The Schengen arrangements had developed outside the original Community treaty structure. They aimed to remove checks at internal borders between participating states while strengthening cooperation concerning external borders, visas and security.

Their incorporation into the EU framework brought the Schengen rules within a more developed institutional and legal structure.

However, participation was not identical for every Member State. Protocols and special arrangements accommodated differences in participation, including the positions of certain states that did not participate in all aspects of Schengen cooperation.

The legal significance of Amsterdam was that Schengen cooperation became integrated into the Union’s treaty-based framework rather than remaining solely an arrangement outside the Communities.

7.3 Expansion of co-decision and qualified majority voting

The treaty extended the co-decision procedure to additional policy areas and expanded the use of qualified majority voting in the Council.

These changes strengthened the European Parliament’s legislative position and reduced the number of areas in which unanimity was required.

The Amsterdam reforms continued the gradual development of a more balanced legislative system in which the Council represented national governments while Parliament represented EU citizens.

7.4 Employment and social policy

The treaty incorporated an employment chapter into the Community framework and strengthened the Union’s ability to coordinate Member State employment policies.

It also developed the legal framework for social policy, equality and non-discrimination. The treaty’s provisions did not create a single European employment system or replace national labour law. Rather, they provided a basis for coordination and for certain common measures within the limits of Community competence.

7.5 The High Representative for the CFSP

Amsterdam created the position of High Representative for the Common Foreign and Security Policy.

The role was intended to improve continuity and visibility in the Union’s external relations. It did not create a fully unified foreign policy or transfer national foreign policy powers wholesale to the Union. Member States retained substantial control over decisions in this field.

Nevertheless, the appointment represented an institutional attempt to make the Union’s foreign policy cooperation more coherent and recognisable.

7.6 Institutional limitations

Although Amsterdam introduced important reforms, it did not resolve all the institutional questions raised by enlargement.

The size and composition of the Commission, the distribution of voting weights in the Council and the broader institutional balance required further adjustment if the Union were to function with a substantially larger membership.

The Amsterdam Treaty therefore represented an important but incomplete stage of constitutional reform. Consilium+2

8. The Treaty of Nice: Institutional Reform for Enlargement (2001–2003)

The Treaty of Nice was signed on 26 February 2001 and entered into force on 1 February 2003. Its principal purpose was to prepare the European Union for enlargement, particularly the accession of states from Central and Eastern Europe.

The anticipated expansion raised a practical institutional question: could a system designed for a relatively small number of Member States continue to operate effectively with a much larger membership?

Nice sought to answer that question by revising the composition of the institutions, the distribution of voting power and certain decision-making procedures.

8.1 Reform of the European Commission

The treaty amended the rules governing the composition of the Commission.

The objective was to preserve the effectiveness and independence of the institution while accommodating an enlarged Union. The reforms concerned the number of Commissioners, the role of the Commission President and the arrangements governing appointments.

The treaty strengthened the President’s position in organising the Commission’s work and allocating responsibilities among its members.

These changes reflected the growing recognition that institutional efficiency depended not only on the number of Member States but also on the internal organisation of the EU institutions.

8.2 Reform of voting in the Council

Nice revised the system of weighted votes in the Council and introduced a more complex arrangement for determining qualified majority decisions.

The reforms sought to balance the interests of larger and smaller Member States while taking account of population and the institutional equality of states.

The system remained complicated and was later replaced by the double-majority system under Lisbon.

Nevertheless, Nice was a significant transitional reform because it attempted to adapt the Council’s voting arrangements to a Union that was about to expand considerably.

8.3 Extension of qualified majority voting

The treaty extended qualified majority voting to additional policy areas.

This was intended to reduce the risk that a larger Council would become unable to adopt legislation because of frequent unanimity requirements.

However, unanimity continued to apply in several sensitive areas, particularly where Member States considered national sovereignty or constitutional identity to be closely involved.

8.4 Enhanced cooperation

The Treaty of Nice also revised the rules on enhanced cooperation.

Enhanced cooperation allows a group of Member States to proceed with integration in a particular field using the Union’s institutional framework, where the treaty conditions are satisfied and the participation requirements are met.

The mechanism was intended to address situations in which all Member States could not or would not proceed at the same pace. It was not designed to permit states to disregard the Treaties or create a separate legal order outside the Union.

Its development reflected the reality that a Union of increasing size might not always be able to advance through identical participation by every Member State.

8.5 Judicial reform

Nice also introduced changes affecting the judicial system of the Communities, including provisions intended to improve the Court of Justice’s capacity to handle an increasing volume of litigation.

The treaty provided for a reorganisation of the judicial architecture and greater flexibility in allocating jurisdiction between the Court of Justice and the Court of First Instance, which later became the General Court.

The reforms were significant because the expansion of EU legislation and membership increased the demands placed on the judicial system.

8.6 The Charter of Fundamental Rights

The Charter of Fundamental Rights of the European Union was proclaimed in 2000, before the Treaty of Nice entered into force.

It brought together a range of civil, political, economic and social rights recognised within the Union’s legal and constitutional traditions.

However, at the time of its original proclamation, the Charter did not yet have the same binding legal status as the Treaties. That status was established later through the Treaty of Lisbon.

The Charter’s development illustrates the distinction between political proclamation and legally binding treaty status. The text existed before Lisbon, but its constitutional position changed significantly in 2009.

8.7 The limits of Nice

The Treaty of Nice addressed institutional questions that had become urgent in anticipation of enlargement. It did not, however, produce a simple or comprehensive constitutional settlement.

Its voting arrangements were technically complex, and the broader question of the Union’s constitutional identity remained unresolved.

These limitations contributed to the subsequent debate on a more comprehensive reform of the European treaties. Consilium+2

9. The Treaty Establishing a Constitution for Europe: The Uncompleted Constitutional Project (2004–2005)

Following the Treaty of Nice, European leaders increasingly recognised that institutional adjustments alone would not settle the deeper questions surrounding the Union’s constitutional structure.

The Union had expanded its responsibilities, developed a substantial body of law and acquired a growing role in the lives of European citizens. Yet its legal foundations remained distributed across several treaties, protocols and institutional arrangements. The three-pillar structure was difficult to understand, and the distinction between the European Union and the European Communities continued to create legal and institutional complexity.

The response was an ambitious attempt to consolidate and reform the Union’s constitutional framework.

9.1 The Convention on the Future of Europe

The Laeken European Council Declaration of December 2001 initiated a process intended to consider the future development of the Union. A Convention on the Future of Europe was subsequently established, bringing together representatives of national governments, national parliaments, the European Parliament and the European Commission.

The Convention prepared a draft treaty intended to simplify the existing legal framework, clarify the distribution of powers and strengthen democratic legitimacy.

The proposed Treaty establishing a Constitution for Europe was adopted by the European Council in June 2004 and signed in Rome on 29 October 2004.

9.2 The proposed constitutional structure

The proposed Constitutional Treaty would have reorganised the existing framework around a single constitutional text.

Its principal features included:

• The replacement of the existing treaty structure with a more unified constitutional instrument.
• The formal abolition of the three-pillar architecture.
• The recognition of the Union’s legal personality.
• A clearer division of competences between the Union and its Member States.
• A more prominent role for the European Parliament.
• A permanent President of the European Council.
• A strengthened external representation role for the Union.
• The incorporation of the Charter of Fundamental Rights into the proposed constitutional text.
• A more extensive application of qualified majority voting.
• A formal procedure for voluntary withdrawal from the Union.

The proposed treaty also sought to make the Union’s legal framework more accessible by consolidating provisions that had previously been distributed across several instruments.

9.3 Why the Constitutional Treaty did not enter into force

The treaty required ratification by all Member States in accordance with their respective constitutional requirements.

Although several Member States approved it, the proposed Constitution was rejected in national referendums in France on 29 May 2005 and in the Netherlands on 1 June 2005.

The negative results prevented the completion of the ratification process. The treaty never entered into force and therefore never became part of the binding constitutional law of the European Union.

It is important to distinguish between the political and legal consequences of this failure. The Constitutional Treaty was a signed international agreement, but signature alone did not make it legally operative. Because the required ratifications were not completed, its provisions did not replace the existing treaties.

9.4 The constitutional debate after the failed treaty

The failure of the Constitutional Treaty led to a period of reflection and renewed negotiations.

The Member States did not abandon the objective of institutional reform. Instead, they sought a different legal method: rather than replacing the existing treaties with a single constitutional document, they would amend the existing treaty framework.

This distinction was politically and legally important. The resulting Treaty of Lisbon retained many of the proposed reforms but avoided adopting the constitutional form and terminology of the failed project.

The Constitutional Treaty therefore occupies an unusual place in EU legal history. It never became binding law, yet it substantially influenced the reforms later incorporated into the Lisbon Treaty. europarl.europa.eu+2

10. The Treaty of Lisbon: The Modern Constitutional Framework (2007–2009)

The Treaty of Lisbon was signed on 13 December 2007 and entered into force on 1 December 2009. It amended the Treaty on European Union and the Treaty establishing the European Community.

Rather than replacing the existing treaties with a single constitutional document, Lisbon revised the established treaty structure. The former Treaty establishing the European Community was renamed the Treaty on the Functioning of the European Union (TFEU), while the Treaty on European Union (TEU) retained its name in revised form.

The result was a substantially reorganised legal framework that continues to form the constitutional foundation of the European Union.

10.1 The abolition of the pillar structure

One of Lisbon’s most important reforms was the abolition of the formal three-pillar structure created by Maastricht.

The European Community was succeeded by the European Union, which acquired a single express legal personality under Article 47 TEU.

This gave the Union the capacity to act as a legal person under international law, including the capacity to conclude international agreements within its competences.

The abolition of the pillar structure simplified the institutional architecture. The Union became a more unified legal entity rather than an organisation operating through formally distinct pillars.

However, the abolition of the pillars did not mean that every policy area became subject to identical procedures. The Common Foreign and Security Policy, for example, retained special decision-making and judicial arrangements. Certain aspects of EU external action therefore continue to operate differently from ordinary internal EU legislation.

10.2 The Treaty on European Union and the Treaty on the Functioning of the European Union

Lisbon established the modern relationship between the two principal EU treaties.

The Treaty on European Union contains the Union’s foundational provisions, including its values, objectives, institutional framework, democratic principles, general provisions on competences and provisions governing external action and foreign and security policy.

The Treaty on the Functioning of the European Union provides more detailed rules concerning the Union’s competences, policies and institutional operation. It addresses matters such as the internal market, competition, agriculture, transport, economic and monetary policy, employment, social policy, environment, consumer protection, freedom, security and justice, and external relations.

The two treaties have equal legal value under Article 1 TEU. Neither is simply subordinate legislation of the other. They must be interpreted together as parts of the Union’s primary law.

10.3 A clearer division of competences

Lisbon clarified the categories of competence exercised by the Union and the Member States.

The Treaties distinguish between:

Exclusive competences: In these areas, the Union alone may legislate and adopt legally binding acts, subject to the treaty framework. Member States may act only where empowered by the Union or where implementing Union law.

Shared competences: Both the Union and the Member States may legislate and adopt legally binding acts. Member States exercise their competence to the extent that the Union has not exercised its own competence, or where the Union has decided to cease exercising it.

Supporting, coordinating or supplementary competences: In these areas, the Union may support or coordinate Member State action but does not generally replace national competence through harmonisation of national laws where the Treaties exclude it.

The principal provisions governing these categories are found in Articles 2–6 TFEU.

The classification was constitutionally important because it made the limits of Union authority more explicit. The EU does not possess a general legislative power comparable to that of a sovereign state. Its authority is derived from the competences conferred upon it by the Member States through the Treaties.

10.4 The European Council becomes a formal institution

Lisbon formally recognised the European Council as an EU institution.

It also created the position of President of the European Council, elected for a renewable term of two and a half years.

The President is responsible for chairing and driving forward the European Council’s work, facilitating cohesion and consensus, and representing the Union at the appropriate level in certain external matters, without prejudice to the responsibilities of the High Representative.

This change gave the European Council greater institutional continuity. Previously, its presidency was linked to the rotating presidency arrangements of the Member States. The permanent President provided a more stable leadership structure.

The distinction between the European Council and the Council of the European Union remains fundamental. The European Council consists of heads of state or government and provides political direction. The Council of the European Union consists of national ministers and participates in adopting legislation and coordinating policies.

10.5 The High Representative and the European External Action Service

Lisbon strengthened the position of the High Representative of the Union for Foreign Affairs and Security Policy.

The High Representative is simultaneously a participant in the Commission as one of its Vice-Presidents and the chair of the Foreign Affairs Council. This dual role was intended to improve coherence between the Union’s external policies and its diplomatic activity.

The treaty also provided for the creation of the European External Action Service (EEAS), which supports the High Representative and contributes to the Union’s diplomatic representation and external relations.

These reforms were designed to improve the consistency and visibility of EU external action. They did not, however, create a single European foreign ministry replacing the foreign ministries of the Member States.

10.6 The European Parliament becomes a more complete co-legislator

Lisbon substantially strengthened the legislative role of the European Parliament.

The co-decision procedure was renamed the ordinary legislative procedure and became the standard procedure for adopting legislation in a much wider range of policy areas.

Under this procedure, the European Parliament and the Council jointly adopt legislation on the basis of a Commission proposal, subject to the rules and exceptions established by the Treaties.

The reform strengthened Parliament’s position in the institutional balance and extended democratic participation in EU law-making.

Lisbon also enhanced Parliament’s role in the budgetary process, giving it a more equal position with the Council in adopting the annual EU budget.

Furthermore, Parliament’s role in the appointment of the Commission President was strengthened. The European Council proposes a candidate, taking account of the European Parliament elections, and Parliament elects the candidate under the procedure set out in Article 17 TEU.

10.7 Qualified majority voting and the double-majority system

Lisbon revised the qualified majority voting system in the Council.

The double-majority system generally requires the support of at least 55% of the Member States, comprising at least 15 states where the Union has 27 members, representing at least 65% of the Union’s population.

The system seeks to balance two principles: the equality of Member States as sovereign participants and the demographic reality that the populations of Member States differ considerably.

A blocking minority generally requires at least four Council members. Where the relevant threshold is not met, the decision cannot be blocked through the ordinary population-based mechanism.

The Treaties provide for exceptions and special voting rules in particular policy areas. Unanimity remains necessary in certain sensitive matters, including some aspects of taxation, foreign policy and treaty revision.

The double-majority system became applicable from 1 November 2014, following a transitional period during which the earlier voting arrangements could still be used.

10.8 The Charter of Fundamental Rights becomes legally binding

One of the most important constitutional changes introduced by Lisbon concerned the legal status of the Charter of Fundamental Rights of the European Union.

Article 6(1) TEU provides that the Charter has the same legal value as the Treaties.

The Charter therefore became a legally binding part of the Union’s primary law framework. It contains rights and principles concerning dignity, freedoms, equality, solidarity, citizens’ rights and justice.

However, its scope must be understood carefully. Under Article 51 of the Charter, its provisions are addressed to EU institutions and bodies and to Member States only when they are implementing or otherwise acting within the scope of EU law.

The Charter does not create a general power for the Union to regulate matters outside its competences, nor does it automatically extend EU fundamental rights review to every action of a Member State.

Lisbon also preserved the separate legal significance of the European Convention on Human Rights. The Treaties provide for the Union’s accession to that Convention, but accession requires the completion of the relevant legal arrangements and is subject to the constitutional requirements established by EU law.

10.9 The European Citizens’ Initiative

Lisbon introduced the European Citizens’ Initiative (ECI), a mechanism of participatory democracy.

It allows a sufficient number of EU citizens from a sufficiently broad range of Member States to invite the European Commission to consider submitting a proposal for a legal act where the Commission has the relevant power to do so.

The ECI does not give citizens a direct power to enact legislation or compel the Commission to submit a proposal. It creates a formal mechanism through which citizens can place an issue on the EU institutional agenda and require the Commission to examine the initiative and provide a response.

The mechanism reflects Lisbon’s broader emphasis on representative and participatory democracy.

10.10 National parliaments and democratic scrutiny

Lisbon strengthened the role of national parliaments in the EU legislative process.

They receive draft legislative acts and may scrutinise whether proposed action complies with the principle of subsidiarity. The associated procedures are commonly known as the early warning mechanism.

Where the required number of national parliamentary votes raises objections, the Commission and other relevant institutions may be required to review the proposal under the applicable procedure.

The reform was intended to connect EU decision-making more closely with national democratic institutions and to reinforce the principle that decisions should be taken at the appropriate level of governance.

10.11 Withdrawal from the European Union: Article 50 TEU

Lisbon introduced an express treaty provision governing voluntary withdrawal from the Union.

Article 50 TEU provides that a Member State may decide to withdraw in accordance with its own constitutional requirements. It must notify the European Council of its intention, after which the Union negotiates an agreement setting out the arrangements for withdrawal, taking account of the framework for its future relationship with the Union.

The Treaties cease to apply to the withdrawing state when the withdrawal agreement enters into force or, in the absence of such an agreement, two years after notification, unless the European Council, in agreement with the state concerned, unanimously decides to extend that period.

The provision became particularly significant during the United Kingdom’s withdrawal process, which culminated in the UK’s departure from the Union on 31 January 2020.

Article 50 is constitutionally important because it confirms that EU membership is not legally irreversible. The Union is a treaty-based legal order whose Member States retain the right to withdraw in accordance with the procedure laid down in the Treaties.

10.12 Euratom after Lisbon

Lisbon did not abolish Euratom or merge its treaty into the TEU or TFEU.

The Euratom Community continues to operate under its own founding treaty, as amended by subsequent reforms. It shares institutions with the European Union, but it retains a separate legal personality and legal framework.

This is an important qualification to the statement that Lisbon created a single legal personality for the Union. The EU became a single legal person in its own right, but Euratom remained a distinct treaty-based Community.

The Lisbon Treaty therefore reorganised the European Union without eliminating every separate legal structure inherited from the earlier Communities. EUR-Lex+3

11. The Treaty Framework in Force: What Constitutes EU Primary Law Today?

The evolution of the treaties produced a legal system in which the foundational rules of the Union are distributed across several instruments. Understanding this structure is essential because EU legislation and institutional action must be consistent with primary law.

11.1 The Treaty on European Union

The TEU establishes the Union’s foundational principles and institutional framework.

It sets out the Union’s values, objectives and general principles, including respect for human dignity, freedom, democracy, equality, the rule of law and human rights.

It also governs the Union’s institutional structure, democratic principles, external action and Common Foreign and Security Policy.

11.2 The Treaty on the Functioning of the European Union

The TFEU provides the detailed rules governing the functioning of the Union and its policies.

It defines the categories of competence, establishes the legal framework for the internal market and regulates many of the Union’s principal policy areas.

It also contains important provisions concerning EU institutions, legislative procedures, competition, economic and monetary policy, social policy, the environment, consumer protection and the Area of Freedom, Security and Justice.

11.3 The Euratom Treaty

The Euratom Treaty remains a separate founding treaty governing the European Atomic Energy Community.

Its continued existence demonstrates that European integration has developed through overlapping legal structures rather than through the complete replacement of every earlier Community.

11.4 Protocols and annexes

Protocols and annexes form an important part of the treaty framework.

They may regulate institutional arrangements, specific policy exceptions, the application of particular provisions to certain Member States, or technical matters that require treaty-level status.

Protocols annexed to the Treaties form an integral part of primary law. They must therefore be considered when interpreting the relevant treaty provisions.

11.5 The Charter of Fundamental Rights

The Charter has the same legal value as the Treaties under Article 6(1) TEU.

It is therefore a central source of primary EU law, although it is not itself a treaty and does not expand the Union’s competences.

11.6 Accession treaties

Accession treaties establish the conditions under which new states join the European Union.

They may contain transitional arrangements, institutional adjustments and specific provisions governing the application of EU law to the new Member State.

Accession treaties form part of the wider primary-law framework and are essential to understanding the legal consequences of enlargement.

EUR-Lex provides access to the texts of the founding, amending and accession treaties, as well as consolidated versions of the current Treaties. EUR-Lex+1

12. How the EU Treaties Are Amended: Article 48 TEU

The treaties are not ordinary legislation. Their amendment requires a procedure involving the Member States and their respective constitutional requirements.

Article 48 TEU establishes the principal procedures for treaty revision.

12.1 The ordinary revision procedure

The ordinary revision procedure is the general method for making substantial amendments to the Treaties.

A Member State government, the European Parliament or the Commission may submit proposals for treaty amendment to the Council. These proposals are transmitted to the European Council and notified to national parliaments.

The European Council may decide, after consulting the European Parliament and the Commission, to examine the proposed amendments through a Convention.

The Convention generally brings together representatives of national parliaments, national governments, the European Parliament and the Commission. It examines the proposals and adopts recommendations by consensus.

A Convention may be omitted where the European Council considers its use unjustified because the extent of the proposed amendments does not warrant it. In that case, the European Council defines the terms of reference for an intergovernmental conference.

An intergovernmental conference, composed of representatives of the governments of the Member States, determines by common accord the amendments to be made to the Treaties.

The amendments enter into force only after ratification by all Member States in accordance with their respective constitutional requirements.

This final requirement is fundamental. A treaty amendment cannot ordinarily become binding EU primary law merely because the EU institutions or a majority of Member States support it.

12.2 The simplified revision procedures

Article 48 also provides simplified revision procedures.

These procedures can be used for certain amendments to Part Three of the TFEU, which concerns the Union’s internal policies and actions, provided that the conditions laid down in Article 48 are satisfied.

The simplified procedure cannot be used to increase the competences conferred on the Union by the Treaties.

The European Council may also adopt certain decisions modifying particular internal provisions, including provisions concerning the Council’s voting arrangements, where the relevant treaty conditions are met.

These procedures remain subject to the applicable requirements, including national approval where the Treaties provide for it.

12.3 Why treaty revision is constitutionally significant

The revision procedure reflects the dual nature of the EU legal order.

The Union has autonomous institutions and a legal system capable of producing binding rules. Nevertheless, its foundational authority derives from treaties concluded and ratified by the Member States.

The EU institutions cannot simply amend the constitutional basis of their own powers through ordinary legislative procedures. The limits of their authority are established by the Treaties, and major changes to those limits require the treaty revision process.

This is one of the clearest expressions of the principle of conferral: the Union may act only within the competences attributed to it by the Member States in the Treaties. EUR-Lex+1

13. The Constitutional Significance of Treaty Evolution

The successive treaty reforms demonstrate that the European Union developed through a process of constitutional transformation without adopting a conventional federal constitution.

Several principles emerge from this history.

13.1 The Union is founded on treaties, but its legal order is autonomous

The EU’s foundational authority derives from international agreements between Member States. However, the legal system created by those agreements has developed characteristics that distinguish it from ordinary international law.

EU law can create rights and obligations for individuals, impose duties on national authorities and require national courts to apply its provisions within the scope of EU law.

The Court of Justice has played a central role in developing this autonomous legal order. Its judgments in Van Gend en Loos (Case 26/62) and Costa v ENEL (Case 6/64) established the foundational doctrines of direct effect and primacy.

The treaties provided the legal framework within which these doctrines developed. They transformed the practical significance of the treaty system by making EU law relevant not only to governments but also to individuals and private organisations.

13.2 Integration has been gradual and treaty-driven

The development of the Union did not follow a predetermined constitutional blueprint.

The Paris Treaty began with a limited sectoral arrangement. Rome expanded integration into the wider economy. The Single European Act accelerated the internal market. Maastricht created the Union and introduced citizenship and monetary union. Amsterdam and Nice adjusted the institutional and policy framework. Lisbon reorganised the legal structure and strengthened the Union’s democratic and institutional arrangements.

Each reform responded to particular political, economic and institutional conditions.

The result is a legal system that contains elements of supranational governance, intergovernmental cooperation and shared constitutional authority.

13.3 The balance between national sovereignty and common authority

The treaties define the relationship between Member State authority and the powers of the Union.

Member States have transferred or conferred the exercise of certain competences upon the EU institutions. In other areas, they retain primary responsibility or share competence with the Union.

The system is therefore not based on the complete displacement of national sovereignty. Nor is it simply a voluntary system of cooperation in which every common decision requires unanimous national approval.

Instead, the Treaties establish a structured allocation of authority, accompanied by rules governing how that authority may be exercised.

13.4 The strengthening of democratic legitimacy

The gradual expansion of the European Parliament’s powers is one of the most visible developments in treaty history.

The original Community system gave national governments and executive institutions a dominant role. Later treaties introduced cooperation, co-decision and ultimately the ordinary legislative procedure.

The European Parliament became a central legislative institution, while national parliaments acquired a more formal role in subsidiarity scrutiny.

The development has not eliminated debates about democratic accountability in the Union. However, it has fundamentally altered the institutional balance compared with the early Communities.

13.5 The constitutional role of the Court of Justice

The Court of Justice has contributed to the interpretation and development of the treaty system.

It ensures that the law is observed in the interpretation and application of the Treaties. Its jurisdiction includes preliminary rulings, infringement proceedings, annulment actions and other procedures established by the Treaties.

The treaty reforms have repeatedly adjusted the Court’s jurisdiction and institutional structure, particularly as the Union expanded its policy responsibilities.

The Court’s case law is therefore indispensable to understanding the practical meaning of the treaties. The written provisions establish the constitutional framework, but judicial interpretation clarifies how that framework operates in concrete legal disputes.

13.6 The limits of integration

Treaty evolution has not resulted in unlimited EU authority.

The Union remains governed by the principle of conferral. It may act only within the competences attributed to it by the Member States. The principles of subsidiarity and proportionality regulate the exercise of non-exclusive competences and the content and form of Union action.

Certain fields, particularly foreign and security policy, continue to involve distinctive intergovernmental features. The Member States also retain important responsibilities in taxation, education, health, criminal justice and other areas, subject to the specific treaty provisions governing EU action.

The history of treaty reform is therefore not simply a story of ever-expanding central authority. It is also a history of negotiation, limitation, institutional balance and the continuing constitutional relationship between the Union and its Member States.

14. Comparative Overview of the Principal European Treaties

The following table summarises the major stages of treaty development and their principal constitutional consequences.

Treaty or reform	Signature / entry into force	Principal legal and institutional contribution
Treaty of Paris	1951 / 1952	Established the ECSC and introduced supranational governance in coal and steel.
Treaties of Rome	1957 / 1958	Established the EEC and Euratom, expanding integration into the wider economy and peaceful nuclear energy.
Merger Treaty	1965 / 1967	Created a single Commission and Council for the three Communities.
First Budgetary Treaty	1970 / 1971	Developed the own-resources system and reformed Community budgetary arrangements.
Second Budgetary Treaty	1975 / 1977	Strengthened Parliament’s budgetary role and established the Court of Auditors.
Single European Act	1986 / 1987	Accelerated the internal market, expanded qualified majority voting and strengthened Parliament’s legislative influence.
Maastricht Treaty	1992 / 1993	Established the European Union, introduced EU citizenship, created the three-pillar structure and laid the foundations for EMU.
Amsterdam Treaty	1997 / 1999	Developed the Area of Freedom, Security and Justice, incorporated Schengen and expanded co-decision.
Nice Treaty	2001 / 2003	Reformed institutions and voting arrangements in preparation for enlargement.
Constitutional Treaty	2004 / Never entered into force	Proposed a unified constitutional framework but failed to complete ratification.
Lisbon Treaty	2007 / 2009	Reorganised the Union’s legal structure, abolished the pillar system, strengthened Parliament and gave the Charter binding legal status.

Dates in the table distinguish signature from entry into force. The Constitutional Treaty is included because of its historical significance, although it never became binding law.

15. Key Takeaways

1. European integration developed through successive treaties. The present EU legal system is the product of gradual institutional and constitutional reform rather than a single founding constitution.

2. The Treaty of Paris established the first supranational Community. The ECSC demonstrated that Member States could entrust common institutions with legally defined powers.

3. The Treaties of Rome expanded integration beyond individual industries. The EEC established the foundations of the common market, while Euratom created a separate framework for peaceful nuclear cooperation.

4. The Merger Treaty consolidated institutions without abolishing the three Communities. It created a single Commission and Council, while their separate legal foundations remained.

5. The Single European Act accelerated the internal market. It expanded qualified majority voting and strengthened the European Parliament’s participation in legislation.

6. The Maastricht Treaty established the European Union. It introduced EU citizenship, the three-pillar structure, Economic and Monetary Union and the foundations for the euro.

7. Amsterdam and Nice prepared the Union for deeper cooperation and enlargement. They developed the Area of Freedom, Security and Justice, expanded legislative procedures and reformed institutional arrangements.

8. The Constitutional Treaty never entered into force. Its proposed constitutional reforms nevertheless influenced the subsequent Lisbon settlement.

9. Lisbon established the modern treaty structure. It gave the EU express legal personality, abolished the formal pillar structure, strengthened Parliament and gave the Charter of Fundamental Rights the same legal value as the Treaties.

10. The current constitutional framework is based principally on the TEU and TFEU. The Euratom Treaty, protocols, annexes, accession instruments and Charter also form important parts of the primary-law framework.

11. Treaty revision remains controlled by the Member States. Article 48 TEU requires compliance with the relevant revision and ratification procedures.

16. Frequently Asked Questions

1. How many founding treaties established European integration?

Three principal founding treaties established the original European Communities: the Treaty of Paris (1951), which created the ECSC, and the two Treaties of Rome (1957), which created the EEC and Euratom.

The Treaty of Maastricht subsequently established the European Union as a broader political and legal framework.

2. Which treaty officially created the European Union?

The Treaty on European Union, signed at Maastricht on 7 February 1992 and entering into force on 1 November 1993, established the European Union.

It brought the European Communities together with new forms of cooperation in foreign policy and justice and home affairs.

3. What was the purpose of the Single European Act?

The Single European Act aimed to complete the internal market by the end of 1992. It expanded qualified majority voting, introduced the cooperation procedure, strengthened Parliament’s influence and gave treaty recognition to European Political Cooperation and the European Council.

4. What was the three-pillar structure established by Maastricht?

The three pillars consisted of:

• The European Communities, which formed the supranational component.
• The Common Foreign and Security Policy, which was predominantly intergovernmental.
• Justice and Home Affairs cooperation, which was also initially predominantly intergovernmental.

The structure was abolished by the Lisbon Treaty, although certain policy areas retained special procedures.

5. Why did the Treaty establishing a Constitution for Europe fail?

The Constitutional Treaty required ratification by all Member States. It was rejected in referendums in France and the Netherlands in 2005, preventing the completion of the ratification process.

The Lisbon Treaty subsequently incorporated many of its proposed institutional reforms through amendments to the existing treaties rather than replacing them with a single constitutional document.

6. Did the Lisbon Treaty create a European federal state?

No. Lisbon substantially strengthened the Union’s legal personality, institutions and legislative framework, but it did not establish a conventional federal state.

The EU remains a treaty-based legal order in which powers are conferred by the Member States. National constitutions and institutions continue to govern substantial areas of public authority.

7. What is the difference between the TEU and the TFEU?

The Treaty on European Union establishes the Union’s foundational principles, objectives, institutional structure and general constitutional framework.

The Treaty on the Functioning of the European Union provides more detailed rules concerning the Union’s competences, policies, legislative procedures and institutional operation.

Both have equal legal value.

8. Does the Charter of Fundamental Rights form part of the EU Treaties?

The Charter is not itself a treaty. However, Article 6(1) TEU gives it the same legal value as the Treaties, making it a binding source of primary EU law.

Its application is governed by Article 51 of the Charter.

9. Can the EU treaties be amended by the European Parliament or Commission alone?

No. The European Parliament and Commission may initiate proposals under the ordinary revision procedure, but they cannot independently amend the Treaties.

The revision procedures under Article 48 TEU involve the Member States and require ratification in accordance with their respective constitutional requirements, subject to the particular rules applicable to simplified revisions.

10. Is the Euratom Treaty still in force?

Yes. Euratom remains a separate treaty-based Community with its own legal personality. It shares institutions with the EU but has not been absorbed into the TEU or TFEU.

11. What is the highest source of law in the European Union?

EU primary law, principally the Treaties, provides the constitutional foundation of the Union’s legal order. Secondary legislation must comply with primary law, and the Court of Justice ensures that the Treaties are interpreted and applied consistently.

12. Can a Member State withdraw from the European Union?

Yes. Article 50 TEU provides a formal withdrawal procedure. A Member State may decide to withdraw in accordance with its own constitutional requirements and must notify the European Council of its intention.

The United Kingdom’s withdrawal demonstrated how this provision operates in practice.

Conclusion

The evolution of the European treaties is the history of a gradual constitutional transformation. What began as a limited economic arrangement governing coal and steel developed into a legal and institutional system with authority over an extensive range of economic, social, political and regulatory matters.

The Treaty of Paris established the principle of supranational cooperation. The Treaties of Rome extended that principle to the common market and peaceful nuclear energy. Institutional and budgetary reforms made the Communities more coherent and financially accountable. The Single European Act accelerated economic integration, while Maastricht transformed the project into a broader Union incorporating citizenship, monetary integration and political cooperation.

Amsterdam and Nice addressed the practical and institutional challenges of deeper cooperation and enlargement. The failed Constitutional Treaty demonstrated the difficulty of establishing a unified constitutional text acceptable to all Member States. Lisbon ultimately achieved a substantial reorganisation through the amendment of the existing treaties rather than their replacement.

The resulting system is constitutionally distinctive. It is founded on international treaties, but it has developed an autonomous legal order whose rules can directly affect individuals, companies, national administrations and courts. Its institutions exercise powers that are neither entirely national nor simply international, while the Member States remain essential participants in the creation, interpretation and development of its constitutional framework.

This dual character is fundamental to understanding EU law. The Union is not merely an organisation through which governments coordinate their policies, but neither is it a sovereign state with unlimited authority. It is a legal and political order established through treaties, governed by the principle of conferral and sustained by a continuing relationship between common European institutions and the constitutional systems of its Member States.

To understand any particular field of EU law, it is therefore necessary to understand the treaties that provide its legal basis. Every regulation, directive, institutional decision and judicial interpretation must ultimately be considered within this constitutional framework.

Principal Legal Sources and Further Reading

The following official materials provide the treaty texts and institutional explanations relevant to this article.

Founding and amending treaties

• EUR-Lex – Treaties of the European Union
• EUR-Lex – Chronological overview of EU treaties
• European Union – Founding agreements
• Council of the European Union – How EU treaties shaped the Council and European Council

Constitutional and institutional development

• European Parliament – History of the Treaties
• European Parliament – Maastricht Treaty
• European Parliament – Treaty establishing a Constitution for Europe (not ratified)
• EUR-Lex – The Treaty of Lisbon
• Council of the European Union – The Treaty on European Union and the Treaty on the Functioning of the European Union

Legislative and constitutional principles

• EUR-Lex – The European Union’s primary law
• Council of the European Union – The ordinary legislative procedure
• European Parliament – The Treaties and the European Parliament’s powers

The current consolidated treaties should be consulted for authoritative legal interpretation:

• Consolidated version of the Treaty on European Union
• Consolidated version of the Treaty on the Functioning of the European Union
• Consolidated version of the Euratom Treaty