Iraqis go to the polls on Saturday to vote in a referendum on the text of a new constitution.
Some Sunni leaders have called for a boycott of the referendum
But members of the once-dominant Sunni Muslim community are being urged to vote against it.
What's the referendum about?
Iraqis are being asked to approve a new constitution for the country. It is part of a political process which was drawn up by Paul Bremer, the senior US civilian administrator in Iraq.
What's at stake?
If the constitution is approved, it will be the text by which the country is governed. It will also pave the way for elections for a new four-year National Assembly to be held by 15 December 2005, and formally ending Iraq's period of transitional government.
How was the constitution drawn up?
A constitution committee sat down to work on the text at the end of May, but it was heavily dominated by Shias and Kurds, which make up the majority in parliament.
To address this imbalance, 15 Sunni Arabs joined the committee in early July.
During the writing of the constitution, Sunni members of the committee complained that they were marginalised. They did not attend the parliamentary session in which the final draft was presented to the National Assembly for approval on 28 August.
What are the controversial areas of the constitution?
The main complaints are:
Federalism and decentralisation: The Kurds have said they want to maintain their autonomous status in the north of the country, and will maintain their regional assembly. Some in the majority Shia community have suggested something similar for themselves in the south. The constitution will allow the Shias to do the same thing in the south after a local referendum.
This would leave Sunni Arabs landlocked in the centre of the country - with access to revenues from current oil fields but cut off from revenues from oil fields developed in the future in the north and south of Iraq.
De-Baathification: The constitution outlaws the Baath, the political party through which Saddam Hussein ruled Iraq. Sunni Arabs fear they may be punished for their past association with a party they had no choice but to belong to.
National Identity: The text says Iraq is "part of the Islamic world and its Arab people are part of the Arab nation" - an apparent concession to non-Arab minorities like the Kurds. Sunnis, and some Shias, wanted the text to say Iraq as a whole is part of the Arab world.
Islam: The text that Islam will be the "basic source of legislation", but balances this with an article that says no law can contradict the "principles of democracy".
Some last-minute changes were made. Will they help?
Three-days of talks in the week before the referendum led to some eleventh-hour changes to the constitution. As a result it has won the backing of at least one Sunni party.
Shias and Kurds agreed to allow the constitution to be reviewed by MPs who are elected in December's elections to take into account Sunni concerns.
What do its supporters say?
They say it is better to have a constitution - even a flawed one - that an elected parliament can work to improve upon in future, than trying to solve all the problems in one go.
If approved, the US, and the UK, are likely to hail it as another major step towards democracy for the Iraqi people. Even if it is rejected, those who participate in the referendum are still engaging in the political process that is a huge step forward for the country after decades of dictatorship, coalition officials have argued.
What do its critics say?
Some Iraqis and analysts argue that, rather than unite the country, the constitution will deepen divisions and fuel the insurgency, not dampen it.
The Brussels-based International Crisis Group recently released a report saying that the charter was not based on broad consent, and the country appeared to be heading towards partition and civil war.
What is the voting process?
More than 6,000 polling sites have been set up around the country by Iraq's Electoral Commission. The polls will be open from 0700 to 1700 local time (0400-1400GMT), although this can be extended if there are any problems such as violence or overcrowding at the stations.
Around 15.5 million of Iraq's 24 million population are registered to vote - higher than the 14.3 million registered to vote in January's elections.
"Do you approve of the draft constitution of Iraq?" is the question voters will be asked. There will be an option of 'yes' or 'no'. The ballot-paper will come in Arabic and Kurdish.
The UN has printed millions of copies of the constitution to be distributed to the public, in many cases from food distribution centres.
Around 500 international observers have registered to monitor the referendum.
How can the constitution be rejected?
Two-thirds of voters in three provinces must reject it for the constitution to fail. Sunni Arabs hold the majority in four of Iraq's provinces.
Sunni leaders have called on their community to reject the constitution, but it is thought many Sunni voters may stay away from polling stations because of violence, intimidation and US military offensives.
A move by the Shia-dominated Iraqi parliament last month to make it harder to reject the constitution - by counting only votes from registered, as opposed to actual voters - was reversed after criticism from the UN and the US.
What about security?
The militant al-Qaeda in Iraq group has called on its supporters to increase attacks ahead of the referendum, and urged Sunnis to boycott the poll.
US President George W Bush warned of a spike in violence, saying: "We can expect they'll do everything in their power to try to stop the march of freedom."
Iraq is putting in place stringent security measures.
Voting is held during a four-day holiday, international and provincial borders will be closed and a night time curfew will be imposed. Travelling in private cars has been banned in some areas and tight security imposed at polling stations.
Despite a similar threat of violence during January's elections, almost 60% of voters turned out to cast their ballot.
What happens next?
Counting of the ballots is expected to take between five to 10 days.
If the constitution is approved, it will be ratified and elections will be on course to be held by the 15 December, with a new government sworn in by 31 December.
If it fails, the National Assembly will be dissolved and elections for a new interim parliament will be held, again by the 15 December. They will then have to write another draft constitution, to go before another referendum by October 2006.