Nov 20, 2006
The session, planned to last a week, has been preceded by discussions over the role of foreign lawyers and public participation in the process.
The issue of whether the defendants can get a fair trial has also been debated.
About two million people died during the years that the Khmer Rouge ruled Cambodia in the 1970s under Pol Pot.
Which of the former Khmer Rouge leaders will be prosecuted first may be announced before the end of the year.
The UN-backed trials are due to start in 2007, and could mean that surviving leaders of the brutal Maoist regime - some of whom are still living freely - will be called to the dock.
The Khmer Rouge trials process started four months ago, but Cambodian and international legal officials still have to agree on many of the procedures for the trials.
Differences in legal systems have to be addressed - not just between local and international laws, but among the various legal codes used by the international officials.
Already the draft rules have been criticised. Human rights groups have warned that the trials could be swamped by a flood of lawsuits from members of the public.
The Cambodian Bar Association has said it will try to block foreign lawyers from representing defendants.
And the principal defender has raised doubts over whether a fair trial is possible for men who have been vilified publicly for more than two decades.
The international co-prosecutor, Robert Petit, says compromise is the only solution.
"We have to adapt the law to our mandate. We have a three year budget, we have some very specific crimes that are by nature extremely complex and difficult to deal with, and we have to adapt those rules and that law so that we can fulfil that mandate," Mr Petit said.
The Pol Pot regime saw up to two million people executed or starved or overworked to death between 1975 and 1979.
Pol Pot, the founder and leader of the Khmer Rouge, died in a camp along the border with Thailand in 1998.
Other key figures have also died. Ta Mok - the regime's military commander and one of Pol Pot's most ruthless henchmen - died on 21 July 2006.
The BBC's Guy De Launey in Phnom Penh says this week's meeting could go a long way to making sure the Khmer Rouge Trials are meaningful to the survivors.