(Reuters) - The 27 countries in the European Union elect the 736 members of the European Parliament this week.
Here are the main election procedures.
* Although the election procedures are to a large extent shaped according to national law and tradition in each member state, each must follow EU rules which ensure the election is by universal suffrage, free and confidential.
* Voting is by proportional representation but each member state chooses whether to use an open or closed list system. On an open list, voters show a preference for one or more candidate. On a closed list, the political parties put their candidates in order of preference and the voter backs one party.
* Most countries have a single constituency or election area but Belgium, Ireland, Italy, France, Poland and Britain have several.
* Voting is compulsory in Belgium, Cyprus, Greece and Luxembourg. Voters must be aged 18 or more in all countries, except Austria, where they can be 16.
* Voting takes place in Britain and the Netherlands on Thursday. Ireland votes on Friday, and Latvia, Cyprus, Malta and Slovakia vote on Saturday. The Czech Republic votes on Friday and Saturday and in Italy voting is on Saturday and Sunday. Voting takes place on Sunday in Austria, Belgium, Bulgaria, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Lithuania, Luxembourg, Poland, Portugal, Romania, Slovenia, Spain and Sweden.
* Each member state elects a number of deputies that is determined by the size of its population. Germany has the highest number (99) and Malta has the lowest (five).
* No results are to be announced until voting has ended in all countries. The European Parliament says the first results will be announced after 2000 GMT on Sunday.
Compiled by Timothy Heritage