The European Union is based on the rule of law. This means that every action taken by the EU is founded on treaties that have been approved voluntarily and democratically by all EU member countries. For example, if a policy area is not cited in a treaty, the Commission cannot propose a law in that area.
A treaty is a binding agreement between EU member countries. It sets out EU objectives, rules for EU institutions, how decisions are made and the relationship between the EU and its member countries.
Treaties are amended to make the EU more efficient and transparent, to prepare for new member countries and to introduce new areas of cooperation – such as the single currency.
Under the treaties, EU institutions can adopt legislation, which the member countries then implement. The complete texts of treaties, legislation, case law and legislative proposals can be viewed using the EUR-Lex database of EU law.
Sorted chronologically from latest to oldest, the main treaties are:
Signed: 13 December 2007
Entered into force: 1 December 2009
Purpose: to make the EU more democratic, more efficient and better able to address global problems, such as climate change, with one voice.
Main changes: more power for the European Parliament, change of voting procedures in the Council, citizens' initiative, a permanent president of the European Council, a new High Representative for Foreign Affairs, a new EU diplomatic service.
The Lisbon treaty clarifies which powers:
- belong to the EU
- belong to EU member countries
- are shared.
The Treaty establishing a constitution for Europe (2004) – with aims similar to the Lisbon Treaty – was signed but never ratified.
Signed: 26 February 2001
Entered into force: 1 February 2003
Purpose: to reform the institutions so that the EU could function efficiently after reaching 25 member countries.
Main changes: methods for changing the composition of the Commission and redefining the voting system in the Council.
Signed: 2 October 1997
Entered into force: 1 May 1999
Purpose: To reform the EU institutions in preparation for the arrival of future member countries.
Main changes: amendment, renumbering and consolidation of EU and EEC treaties. More transparent decision-making (increased use of the ordinary legislative procedure).
Signed: 7 February 1992
Entered into force: 1 November 1993
Purpose: to prepare for European Monetary Union and introduce elements of a political union (citizenship, common foreign and internal affairs policy).
Main changes: establishment of the European Union and introduction of the co-decision procedure, giving Parliament more say in decision-making. New forms of cooperation between EU governments – for example on defence and justice and home affairs.
Signed: 17 February 1986 (Luxembourg) / 28 February 1986 (The Hague)
Entered into force: 1 July 1987
Purpose: to reform the institutions in preparation for Portugal and Spain's membership and speed up decision-making in preparation for the single market.
Main changes: extension of qualified majority voting in the Council (making it harder for a single country to veto proposed legislation), creation of the cooperation and assent procedures, giving Parliament more influence.
Signed: 8 April 1965
Entered into force: 1 July 1967
Purpose: to streamline the European institutions.
Main changes: creation of a single Commission and a single Council to serve the then three European Communities (EEC, Euratom, ECSC). Repealed by the Treaty of Amsterdam.
Signed: 25 March 1957
Entered into force: 1 January 1958
Purpose: to set up the European Economic Community (EEC) and the European Atomic Energy Community (Euratom).
Main changes: extension of European integration to include general economic cooperation.
Signed: 18 April 1951
Entered into force: 23 July 1952
Expired: 23 July 2002
Purpose: to create interdependence in coal and steel so that one country could no longer mobilise its armed forces without others knowing. This eased distrust and tensions after WWII. The ECSC treaty expired in 2002.
When new countries joined the EU, the founding treaties were amended:
- 2013 (Croatia)
- 2007 (Bulgaria, Romania)
- 2004 (Czechia, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, Slovenia)
- 1995 (Austria, Finland, Sweden)
- 1986 (Spain, Portugal)
- 1981 (Greece)
- 1973 (Denmark, Ireland, United Kingdom).