Austrians have returned to the polls to decide the presidential race between a right-wing populist and his left-leaning rival. The vote is being watched, as a far-right win could boost populist movements in Europe.
Most polling stations opened at 7 a.m. (0600 UTC) and will close by 5 p.m. on Sunday. Results are expected to arrive later in the evening, but the winner may not be known until absentee ballots are tallied on Monday.
Van der Bellen, a former Greens party leader, narrowly won the first run-off election in May when he received 50.3 percent of the vote - less than 31,000 votes ahead of Hofer.
Austria decides - The populist challenge
The Freedom Party successfully appealed the result by presenting evidence of ballot counting irregularities, winning a repetition of the election.
Voter surveys indicate Sunday's race will also be close. With 20 percent fewer postal votes this time around, Hofer might have a slight advantage.
Although the presidency in Austria is a mostly ceremonial role, the results are sure to reverberate across Europe, as a win by Hofer could boost other populist, euroskeptic movements in next year's elections in France, Germany and the Netherlands.
It would also make Hofer the first far-right elected president since World War II.
Hofer's FPÖ party has been leading opinion polls for months and is set to win the next parliamentary election, according to voter surveys.
End of a bitter campaign
Van der Bellen, a 72-year-old economics professor, is running as an independent although he has the backing of the Greens party. He is a pro-European liberal who aspires to a fence-free "United States of Europe" and is a supporter of gay marriage. He has garnered the support of young Austrians and celebrities, calling for the country to be guided by "reasons not extremes."
Hofer, a 45-year-old engineer and gun-enthusiast, has stoked and benefited from a growing sense of unease in Austria over globalization and multiculturalism. In May, he told a young Austrian Muslim on a talk show that Islam "has no place in Austria" as it threatens Austria's Judeo-Christian values.
He has also said he wants a "Europe of fatherlands" or a less "centralized" form of the EU. Hofer has also said he would call for a referendum on Austria's EU membership if Turkey joins the bloc or if Brussels takes too much power from member states.
Despite its largely ceremonial role, the Austrian constitution grants the president several previously unused powers such as dismissing the government.
Austria's vote also comes on the same day as a high-stakes referendum in Italy which will decide the political fate of Prime Minister Matteo Renzi. It could also renew chaos in a bloc already rattled by the United Kingdom's June vote to leave the EU and Donald Trump's surprising electoral win in the US.