Saddam Hussein is going on trial in Baghdad for crimes against humanity.
Saddam Hussein's lawyers contest the legitimacy of the court
The former Iraqi leader will be led into court with seven associates, charged with ordering the killing of 143 Shia men in 1982.
His lawyer Khalil Dulaimi said the trial was illegitimate and he would ask for an adjournment, but said Saddam Hussein was still "very optimistic".
The case - filmed by TV cameras - will be heard in a specially built courtroom in the heavily fortified Green Zone.
The ex-leader's followers have called for attacks to mark the trial's start.
An internet statement attributed to the Baath party urged supporters to "salute the leader... by firing bullets and mortars of death at the occupier".
Mr Dulaimi told the Associated Press on Tuesday evening: "I have just left him [Saddam] five minutes ago. His morale is very, very, very high and he is very optimistic and confident of his innocence, although the court is... unjust."
The lawyer said that when the trial opened he would ask the court for an adjournment of at least three months, to allow him more time to prepare the defence case.
Court officials say that after legal argument an adjournment is likely to be granted, though it is not clear for how long.
The trial is presided over by five judges, whose identities and backgrounds have been kept secret.
A small number of observers and journalists will be in the televised courtroom, but the public will be excluded.
The case is the first of many expected to be brought against the former Iraqi leader.
Saddam will be led to the dock amid high security
It concerns the rounding up and execution of 143 men in Dujail, a Shia village north of Baghdad, following an attempt there on Saddam Hussein's life.
Court officials say the case was chosen because it was the easiest and quickest case to compile.
The charge carries the death penalty, though Saddam Hussein and his associates have the right to appeal if they are found guilty.
Prosecution lawyers are also expected to bring charges concerning the gassing of 5,000 people in the Kurdish village of Halabja in March 1988, and the suppression of a Shia revolt following the first Gulf War.
SADDAM IN CUSTODY
13 December 2003 Saddam captured by US forces
20 April 2004 Tribunal set up to try Saddam
1 July 2004 Saddam appears before judge for first time
20 May 2005 Photos of Saddam in his underpants appear in a British newspaper
30 July 2005 Saddam's lawyers allege he has been assaulted by a man after leaving a legal hearing
Iran said on Tuesday it had asked the court to charge the former Iraqi leader over the use of chemical weapons in the 1980-88 Iran-Iraq war.
Saddam Hussein's lawyers are expected to challenge the court's right to conduct the trial.
"We will dispute the legitimacy of the court as we've been doing every day. We will claim it is unconstitutional and not competent to try the legitimate president of Iraq," Mr Dulaimi said.
Human rights groups, too, have expressed concerns.
A Human Rights Watch report says the Iraqi Special Tribunal "runs the risk of violating international standards for fair trials".
Amnesty International said it was sending three delegates to Baghdad to ensure Saddam Hussein received a fair trial, and to oppose the death penalty if he is found guilty.
But the United States said it expected the trial - the first time an Arab leader has been tried for crimes against his own people - to meet "basic international standards".