France is set to vote in a run-off poll that could see a socialist win a French presidential election for the first time since 1988.
In the first round socialist Francois Hollande won 28.6% of the vote, ahead of incumbent Nicolas Sarkozy on 26.2%.
Rising unemployment and the euro crisis have dominated the campaign.
Mr Sarkozy says he averted recession and will preserve a “strong France”. Mr Hollande contends the country is in “serious crisis” and needs change.
Polls in mainland France and Corsica will be open from 08:00 to 18:00 (06:00-16:00 GMT), with voting stations in big cities remaining open for another two hours.
On Wednesday the two rivals took part in a testy debate, watched by an estimated 17.9 million people, and continued to campaign until Friday.
Mr Hollande – who has long been regarded as favourite – said turnout on election day could affect the result.
Mr Sarkozy said no election had ever been so “undecided”.