Who's voting? 15.7 million of Iraq's 26 million citizens are eligible to vote in today's referendum on the constitution.
Participation could be similar to the January 2005 parliamentary election when 58 per cent voted nationwide, with highest turnout in the Kurdish north, followed by the Shia south and a substantial boycott in the central Sunni region of the country.
What's at stake? With US fatalities in Iraq approaching 2,000, the Bush administration wants to demonstrate that nation-building is succeeding in Iraq. The interim Iraqi government will interpret a Yes victory as a plebiscite in its favour.
The most salient feature of the constitution is the extensive powers it grants to regions - a precursor to the break-up of Iraq, in the opinion of critics. The US military fear it could aggravate violence in disaffected Sunni areas.
What happens next? If the constitution fails, foreign minister Hoshyar Zibari predicts "total chaos". The parliament elected in January would be dissolved and a new parliament elected to start drafting a constitution all over again.
If, as expected, the constitution passes, Iraq will hold parliamentary elections on December 15th, and a new government will be chosen. Sunni deputies would have four months to seek amendments to the present constitution, which would have to be approved in another referendum. Iraqi officials say the establishment of a full-term government would enable the US to begin planning a troop withdrawal.