European elections culminate on "Super Sunday" when the remainder of the EU's 28 countries go to the polls, with the vote expected to confirm the dominance of pro-EU centrists despite a rise in support for the far-right and left.
Germany, France, Spain, Italy and Poland are among the major EU member states voting on Sunday, representing the bulk of the 388 million Europeans eligible to cast ballots and elect the 751 deputies to sit in the European Parliament from 2014-2019.
After years of economic crisis, rising unemployment and poor growth, many Europeans have come to question the wisdom of ever-closer EU integration and are expected to vote for Eurosceptic parties on the right or left that promise radical change.
Elections have already taken place in seven EU member states, including the UK, the Netherlands, Latvia and Malta. Results will be announced after the last poll closes at 21:00 GMT.
Opinion polls suggest at least a quarter of seats in the parliament will go to anti-EU or protest groups, but at least 70 percent will remain with the four mainstream, pro-EU blocs: the centre-left, centre-right, liberals and Greens.
Turnout - the most basic measure of citizens' engagement with Europe - is expected to fall again, dropping to just over 40 percent, marginally down from 43 percent in 2009.
The 751 seats of European Parliament are allocated in proportion to each country's population.
The vote will affect the lives of the EU's 500 million citizens, and the chamber has much more power than it used to.