Every action is based on the "subsidiarity principle", according to which the Union should not intervene unless Community action would be more effective than national, regional or local action.

• The European Parliament : elected every five years has 626 MEPs affiliated to transnational political groups. Plenary sessions, which all MEPs attend, are held in Strasbourg, the Parliament's seat. Parliamentary committee meetings and any additional plenary sessions are held in Brussels, whilst the General Secretariat is in Luxembourg.
  - it exercises democratic control over all the Community institutions, in particular the Commission ;
  - it shares legislative power with the Council ;
  - it plays a decisive role in the adoption of the budget.
• The Council of the European Union : it represents the Member States. Its seat is in Brussels, where the ministerial meetings take place, except in April, June and October, when they are held in Luxembourg.
  It comprises one ministerial level representative of each Member State, empowered to commit his or her government. The Presidency of the Council is held for six months by each of the Member States in turn.
  As an executive body, it has three essential roles :
  - decision-making ;
  - coordinating the economic policies of the Member States; ;
  - sharing the budgetary function with the European Parliament.
• The European Commission : the executive body with the right to initiate draft legislation, its seat is in Brussels.
  Its 20 members are chosen for their general competence, and all present guarantees of independence. The Commission is reappointed every five years, within six months of the elections to the European Parliament.
  - it proposes legislation to Parliament and the Council ;
  - it administers and implement Community policies ;
  - it enforces Community law (jointly with the Court of Justice) ;
  - it acts as a mouthpiece for the European Union and negotiate international agreements, Maynly those relating to trade and cooperation.
• The Court of Justice : ensures that Community law is uniformly observed. Its seat is in Luxembourg. It comprises one judge per Member State aided by eight advocates-general, they are appointed by joint agreement of the governments of the Member States for a renewable term of six years, with partial reappointment every three years.
• The Court of Auditors : checks that financial management of the EU budget has been sound, and complies with law. Its seat is in Luxembourg. It comprises 15 members appointed by the Council for a renewable term of six years, ruling unanimously after consultation with the European Parliament.
• The European Economic and Social Committee : is an advisory body ensuring that the various economic and social interest groups (employers, trade unions, farmers, consumers, etc.) are represented in the institutional framework of the European Union. Its seat is in Brussels. The 222 members whose distribution approximately reflects the population size are appointed for a renewable term of four years.
  
• The Committee of the Regions : allows representatives of local and regional authorities to give opinions on European Union policies in the matter of agriculture, protection of the environment or urban policy. The 222 members of the Committee and the same number of alternates are nominated by the Council of the European Union for a renewable term of four years, at the recommendation of the respective Member States. Their seat is in Brussels, and they are allocated to 6 specialist commissions.
  
• The European Ombudsman : receives complaints from EU citizens or natural or legal persons if they consider that they have been harmed by an act of "maladministration" by an EU institution or body. He is appointed for a renewable term of five years, and is assisted by a secretariat. His seat is in Strasbourg.
  
• The European Investment Bank (EIB) : funds public and private investment in projects that promote the objectives of European integration. Its seat is in Luxembourg. Non-profit-making, it is financed through borrowing on the financial markets.
  
• The European Central Bank : frames and implements European monetary policy; it conducts foreign exchange operations. Its seat is in Frankfurt am Main. It works in close collaboration with the national central banks, but enjoys total independence..
  

Austria, Belgium, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Nederland, Portugal, Spain.