Turnout for Sunday's hotly fought election between Prime Minister Yulia Tymoshenko and opposition leader Viktor Yanukovych is expected to be high
Ukraine is holding a run-off vote in the country's first presidential election since the 2004 Orange Revolution, which brought pro-Western reformer Viktor Yushchenko to power.
Opposition leader Viktor Yanukovych faces Prime Minister Yulia Tymoshenko in the vote after neither candidate won more than 50% in January's first round. They won 35% and 25% of votes respectively.
President Yushchenko, the one-time hero of the Orange Revolution, came fifth out of a field of 18 candidates, winning just 5.5% of votes.
Who are the main candidates?
Opposition leader Viktor Yanukovych
Viktor Yanukovych led his rival by 10% in the first round
President Yushchenko's Kremlin-backed rival in 2004, Mr Yanukovych won the election but was ousted after the poll was declared fraudulent, sparking the Orange Revolution which swept his opponent to power. However, the former prime minister remains Ukraine's most popular politician, while continuing to inspire much distrust outside his traditional support base in the east and south of the country. Mr Yanukovych has based his campaign on rejection of the legacy of the Orange Revolution and criticism of Prime Minister Tymoshenko's handling of the economy, which has been badly hit by the world financial crisis. His manifesto promises economic reform and improved social standards. It devotes relatively little attention to foreign policy, but promises to restore friendly relations with Russia and stay out of Nato.
Prime Minister Yulia Tymoshenko
Tymoshenko is Ukraine's most flamboyant and charismatic politician
A driving force behind the Orange Revolution, Mrs Tymoshenko is Ukraine's most flamboyant and charismatic politician. Her second term as prime minister, which began in December 2007, has been marked by constant conflict with President Yushchenko. Mrs Tymoshenko's manifesto focuses on fighting "oligarchy" and creating a "just society", and calls for European standards of democracy, while building friendly relations with Russia.
President Viktor Yushchenko
Outgoing President Viktor Yushchenko saw his support dwindle
Mr Yushchenko has said he will not support either candidate in Sunday's run-off vote. Despite having won the presidency on a wave of popular enthusiasm, he did not fulfill election promises to eradicate corruption, introduce transparent government and set the country on a path towards EU membership. Although there has been progress in democratisation and media freedom, his presidency has been marked by domestic political deadlock, deteriorating relations with Russia and growing frustration in Brussels and Washington.
What do opinion polls say?
Ukrainian law forbids publication of opinion poll data in the two weeks before election day. Polls taken before the first round of voting suggested Mr Yanukovych would win a runoff against Mrs Tymoshenko by 10-15 percentage points. However, with around a fifth of respondents saying that they were undecided or against both candidates, Mrs Tymoshenko still appears to have a chance of closing the gap. She has always been a highly effective campaigner and her bloc has consistently performed better in parliamentary elections than polls predicted. If the result is close, either loser is likely to challenge it through the courts and try to rally protests in streets and squares, as during the Orange Revolution - if on a smaller scale. Turn-out is expected to be in the range of 75%, higher than in the first round.
What is Russia's position?
In 2004, then President Vladimir Putin endorsed Mr Yanukovych ahead of the first round. This time Russia has not openly backed any of the candidates, though its leaders have made clear that it will be glad to see the end of Mr Yushchenko's presidency. During his annual conversation with the nation in December, Prime Minister Putin denied suggestions that he favoured Mrs Tymoshenko, whom he has described as a person with whom he can do business, and noted the close relations between the ruling United Russia party and Mr Yanukovych's Party of Regions. As the campaign progressed, coverage of the election on state-controlled Russian TV channels moved from being fairly even-handed between Mr Yanukovych and Mrs Tymoshenko towards a more clearly pro-Yanukovych slant.
What are the powers of the presidency?
Under former President Leonid Kuchma, Ukraine had a strong presidential system of government. A constitutional reform package that was adopted as a compromise during the Orange Revolution and came into force in January 2006 transferred some powers from the president to parliament. The imperfection of these reforms has been widely blamed for the dysfunctional governance in recent years. Mrs Tymoshenko has said that if elected, she will seek a return to the strong presidency of the Kuchma years. Mr Yanukovych has spoken of the need for reforms within the current parliamentary-presidential model, to clarify the division of powers.
What are the election rules?
The president is elected by popular ballot for five years. Presidential candidates must be citizens of Ukraine, at least 35 years old and have resided in Ukraine for at least 10 years. They are also required to be able to speak Ukrainian. There is no minimum turnout requirement. Three days ahead of the run-off vote, Mr Yushchenko signed into law a change in electoral legislation that allows vote-counting at polling stations to go ahead whether or not representatives of both candidates were present. Mrs Tymoshenko said the change would help supporters of her opponent commit fraud. Mr Yanukovych dismissed his rival's complaints, saying they smacked of desperation.
Will the poll be fair?
There is widespread public scepticism about the fairness of the election, despite the first round of voting being given a clean bill of health by independent monitors. An opinion poll ahead of the first round suggested around 40% of Ukrainians expect vote-rigging to affect the outcome of the election. Throughout the campaign, Mr Yanukovych and Mrs Tymoshenko have repeatedly accused each other of plotting to rig the election.
BBC Monitoringselects and translates news from radio, television, press, news agencies and the internet from 150 countries in more than 70 languages. It is based in Caversham, UK, and has several bureaux abroad.