Leonid Kuchma is stepping down after two terms
Ukrainians go to the polls on Sunday to elect their third president since independence, following a bitterly contested campaign and amid worries over security.
The two frontrunners are expected to go to a second round in November.
Q: What is at stake?
President Leonid Kuchma has run the country as prime minister, then head of state, since 1993.
Now he is bowing out, despite a controversial Constitutional Court decision allowing him to run again.
The incoming president will have a major say in deciding whether Ukraine moves closer to the European Union or to a newly-reassertive Russia.
Q: Who is standing?
A total of 26 candidates were registered by the 6 August deadline but several have since dropped out.
Barring an upset, the winner will be the current prime minister, Viktor Yanukovych, or a former prime minister and leader of the centre-right Our Ukraine opposition, Viktor Yushchenko.
Other candidates stand little chance. Observers say many are "decoys", nominated to secure seats on local election boards for the frontrunners.
However, Communist leader Petro Symonenko and Socialist leader Oleskandr Moroz are not without influence, and the distribution of their support in round two could prove decisive.
Independent poll on 15 Oct
Yanukovych - 31.4%
Yushchenko - 29%
Moroz - 4.4%
Symonenko - 3.2%
Yanukovych - 38.5%
Yushchenko - 37.3%
Undecided - 14.3%
Q: What do opinion polls say?
Two recent polls - one by the independent Democratic Initiatives Fund and the other by the pro-government Kiev Centre for Political and Conflict Studies - show Mr Yanukovych ahead in both rounds.
In the independent poll, however, the gap is significantly narrower.
Q: What does the president do?
The president has the power to appoint and dismiss ministers and regional governors, and to initiate legislation.
The government, the Socialists and the Communists have been pressing for reforms that would transfer more power to parliament.
But the government's own bloc of parties recently split, losing its majority in parliament. The centre-right opposition opposes a watering down of the presidency.
Pro-government poll on 12 Oct
Yanukovych - 34.4%
Yushchenko - 31%
Moroz - 6.7%
Symonenko - 5.8%
Yanukovych - 41.9%
Yushchenko - 37.1%
Undecided - 8.8%
Q: What is the system?
To win outright in round one a candidate must gain over 50% of the vote, otherwise a runoff is held between the two leaders. There is no minimum turnout requirement.
All Ukrainian citizens aged 18 and above can vote. There are about 36 million registered voters.
Candidates with criminal records are barred. Mr Yanukovych served two prison terms in his youth, but says the convictions were quashed. The opposition has made this a campaign issue.
Q: How was the campaign?
The two main rivals have traded insults and recriminations. Mr Yushchenko twice accused the authorities of trying to kill him.
The authorities denied this and accused pro-Yushchenko groups of plotting "terrorist attacks", such as the bombing of a major Kiev market in August.
Mr Yanukovych and Mr Yushchenko both say they will boost economic growth, create jobs, maintain good relations with Russia and the West, respect the Russian language and withdraw peacekeepers from Iraq.
They differ in emphasis, with Mr Yushchenko calling for an immediate troop withdrawal.
He also wants a war against the "bandits" he says are using the government to enrich themselves through privatisation and corruption.
Mr Yanukovych stresses closer ties with Russia and pits his patriotism against Mr Yushchenko's alleged "nationalism".
Q: What of the media?
Leading TV channels UT1, Inter and 1 +1 - linked to a senior presidential aide - have given Mr Yanukovych glowing coverage and tended to disparage Mr Yushchenko.
The less popular ICTV, Novyy Kanal and STB channels - owned by President Kuchma's son-in-law - have been fairer to Mr Yushchenko, while still favouring Mr Yanukovych.
Only one national channel, 5 Kanal, gave prominence to Mr Yushchenko. It is owned by a Yushchenko ally and has been facing closure, following what it calls a government campaign against it.
Radio stations critical of the government have had their licences withdrawn. There is a wider range of opinion in the press, with popular papers often polarised in their views.
Q: Will the vote be fair?
Observers are worried by reports of deceased Ukrainians on electoral registers and by claims that local authorities act on Mr Yanukovych's behalf.
The opposition says most local election boards are staffed by the prime minister's allies.
Q: Who monitors the poll?
The candidates themselves, and registered foreign observers, can nominate monitors.
Independent domestic observers are not allowed, and local rights groups have complained of the predominance of pro-government monitors.
The Organisation for Security and Cooperation (OSCE) is sending about 600 observers.
Q: What's the view from abroad?
Until remarks by President Putin just days before the election, Moscow declined to comment directly.
There is little evidence that Russia's state-run media will turn on the Ukrainian authorities, even in the event of a compromised vote.
The United States and the European Union have made it clear that a fraudulent election will damage relations.
BBC Monitoring, based in Caversham in southern England, selects and translates information from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages.