Ukrainians are voting in the second round of an election that could thrust a comedian with no prior political experience into the presidency of a country at war and wanting transformational change.
Volodymyr Zelenskiy, who plays a fictitious president in a popular TV series, has led opinion polls against the incumbent Petro Poroshenko, whose popularity has been dragged down by patchy efforts to tackle corruption and sliding living standards.
At stake is the leadership of a country on the frontline of the West's standoff with Russia following the 2014 Maidan street protests and the annexation of Crimea.
Both candidates have pledged to keep the country on a pro-Western course.
Investors are also seeking reassurances that whoever wins will accelerate reforms that are needed to keep foreign aid flowing and attract much-wanted foreign investment.
Mr Zelenskiy's promise to fight corruption has resonated with Ukrainians who are fed up with politics as usual in a country of 42 million people that remains one of Europe's poorest nearly three decades after winning independence from the Soviet Union.
His rise comes at a time of political insurgency in many parts of the world, from Brexit to the election of US President Donald Trump and to the 5-Star Movement in Italy, which was also driven by a comedian.
"I think the top election issue is frustration with the status quo," said Mary O'Hagan, Ukraine Resident Senior Director of the National Democratic Institute.
Mr Poroshenko was elected amid high hopes for change after the Maidan protests.
Ms O'Hagan says he inherited a difficult situation in 2014 and implemented many reforms but has not convinced voters that he is serious about tackling corruption.
"I think it is fair to say that public opinion has not regarded the current set-up as a sufficient step forward from what there was before, to justify the many sacrifices that people have made following the revolution, in terms of living standards, security, loss of life, displacement," she said.
Mr Zelenskiy's unorthodox campaign has relied heavily on quirky social media posts and comedy gigs instead of traditional rallies and leaflets.
Mr Poroshenko has sought to portray his rival as a buffoonish populist whose incompetence would leave Ukraine vulnerable to Russia. Ukrainian troops have battled Kremlin-backed separatist fighters since 2014 in a conflict in the eastern Donbass region that has killed 13,000 people despite a notional ceasefire.
A victory for Mr Zelenskiy would be a drastic departure from previous presidential elections in independent Ukraine, which were won by experienced politicians including three former prime ministers.
However he remains something of an unknown quantity and faces scrutiny over his ties to a powerful oligarch who would like to see Mr Poroshenko out of power.
Just 9% of Ukrainians have confidence in their national government, the lowest of any electorate in the world, according to a Gallup poll published in March.