The 27 countries in the European Union elect the 736 members of the European Parliament this week.
Here are some facts about the election and the assembly.
Q. Who votes and when?
A. More than 375 million people are eligible to vote in the 27 European Union member states. Voting is taking place over four days, having starting in Britain and the Netherlands yesterday.
Ireland votes today, and Latvia, Cyprus, Malta and Slovakia vote tomorrow.
Two countries vote over two days -- the Czech Republic on Friday and Saturday and Italy on Saturday and Sunday.
Voting takes place on Sunday in the rest of the member states -- Austria, Belgium, Bulgaria, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Lithuania, Luxembourg, Poland, Portugal, Romania, Slovenia, Spain and Sweden.
Voting is by secret ballot. Results cannot be released by any country until voting ends in all member states. Since the last election in 2004, Romania and Bulgaria have joined the EU.
Q. Who will be elected?
A. The voters choose 736 members of parliament (MEPs) for a five-year term. Each member state is allocated a number of representatives based on the size of its population. Germany, which has the largest population, will have the largest number of MEPs after the election (99), followed by Britain, France and Italy with 72. Malta will have the fewest -- five.
Once in parliament, MEPs are grouped according to their political alliance. After this election each group must have a minimum of 25 MEPs representing at least seven member states.
The number of MEPs in the outgoing parliament was 783. The main force was the European People's Party and European Democrats, followed by the Party of European Socialists and then the Alliance of Liberals and Democrats.
Under the EU's Lisbon reform treaty, which will eventually go into force after the election if it is approved by all member states, the number of MEPs would rise temporarily to 754.
Q. What is the European Parliament?
A. The parliament is one of the three main EU institutions and its role is to represent the interests of EU citizens. The other main institutions are the Council of the European Union and the European Commission.
The Council is the EU's main decision-making body, has one representative from the government of each member state and sets overall policy. The Commission is the EU's executive arm, responsible for implementing the decisions of the parliament and Council. It also has one representative from each member state.
The European Parliament meets in Brussels and the French city of Strasbourg. It was established in 1952 but has changed a great deal since then and is the only European institution that is directly elected -- under procedures introduced in 1979. Before then MEPs were appointed by national governments.
Q. What does the European Parliament do?
A. The parliament has three main roles -- passing European laws, democratic supervision of the other EU institutions and authority, with the Council, over the Union's budget.
The parliament shares power equally with the Council on about two-thirds of proposals for EU legislation under a procedure known as co-decision. In some fields, such as agriculture, economic policy, visas and immigration, the Council alone legislates but must consult the parliament.
The EU's annual budget is decided jointly by the parliament and Council, and a parliamentary committee monitors how the budget is spent.
The parliament can veto the appointment of the European Commission, whose members cannot be appointed without parliamentary approval. The parliament also monitors the work of the Council and can set up committees of inquiry based on petitions by EU citizens.
Q. How will the parliament be affected by the Lisbon treaty?
A. If the EU's reform treaty is approved, the number of MEPs will be reduced and parliament's powers will be enhanced.
Co-decision would be extended to include such areas as agriculture, fisheries, legal migration, space and sport.
Parliament's budgetary powers would be extended to all EU expenditure. Parliament would have more powers over the appointment of the president of the Commission.