Monday, 19 January 2009
Kaing Guek Eav - better known as Comrade Duch - will be the first in the dock, facing charges of crimes against humanity and war crimes.
He ran Tuol Sleng prison, where detainees were tortured and executed.
As many as two million people are thought to have died during the Khmer Rouge government in the late 1970s.
The process of bringing the regime's leaders to court has suffered years of procedural delays, and no major figures have yet stood trial.
Brutal Khmer Rouge regime
Duch was in charge of the notorious facility known as S-21 or Tuol Sleng, where about 15,000 prisoners were systematically tortured.
Those who survived the ordeal were sent for execution in the so-called "killing fields".
Officials have indicated that Duch cooperated with the investigating judges and is willing to testify in court, so correspondents say the trial should be a chance for survivors of the Khmer Rouge era to hear directly at last from one of the organisation's key figures.