Since the first European election in 1979, voter turnout has been in steady decline.
The overall turnout figure in 1979 was 63%; in 2004 it was 45.7%. These figures mask very different participation rates between different member countries: turnout in Slovakia was 17% in 2004, compared with 73% in Italy.
It was also high in Belgium, Greece and Luxembourg, where voting is compulsory.
Over the same period, the number of people participating in national elections has also tended to drop, in some cases by 10% or more.
While 76% of voters cast ballots in the UK's 1979 general election, only 59% turned out in 2001. In France, 71% voted in the 1980 parliamentary poll, compared with 60% in 2002.
However, participation in European elections is lower than in national elections - by an average of 22% in the 15 older member states. In the new member states, which voted for the first time in the 2004 European election, this turnout gap averaged 29%.
In the new member states, on average, only 27% of the electorate cast a vote in the 2004 election. In the other 15, turnout was 49.4% - about one half of a per cent down on 1999.