There was uncertainty as to whether the trial would begin when Colonel Theoneste Bagosora and fellow Rwandan army commanders, Anatole Nsengiyumva, Aloys Ntabakuze and Gratien Kabiligi refused to leave their cells and enter the dock.
The four defendants are charged with 10 to 12 counts of genocide, crimes against humanity, and rape.
The former Rwandan soldiers argued that their trial should be postponed because they had not been given French translations of key documents and witness statements.
After several hours of debate, the court ruled that the prosecutor could proceed with an opening statement. But witnesses cannot testify until documents related to them are translated.
In her opening statement, U-N Chief Prosecutor Carla Del Ponte emphasized the magnitude of the crimes that occurred in Rwanda in 1994.
Prosecution spokesman Tom Kennedy explains.
"She said that these crimes touch every one of us wherever we live because they offend against our deepest principles of human rights and human dignity. She then said that certain of the charges against the four accused are appalling by reason of their violence and their cruelty. Other charges reveal a plan, an organization and coldly concerted acts".
This is the most important case to come before the International Criminal Tribunal for Rwanda, based in the Tanzanian town of Arusha.
Mr. Kennedy says Mrs. Del Ponte believes the four men on trial conceived and implemented the plan to slaughter about 800-thousand fellow Rwandans.
She regards this as a key trial because what she is saying is that the agreement, the conspiracy, between these four defendants was actually at the heart of the genocide. They are the ones that were really the mastermind behind the genocide and the motor, the driving force of it, including distributing weapons, training Interahamwe militias, and so forth in the years running up to the commission of the genocide.
The Interahamwe was a Hutu militia, which was at the forefront of the slaughter of Tutsis and moderate Hutu's in Rwanda.
About 250 witnesses will be called during the next two-years. The majority of them are genocide survivors who are allowed to testify anonymously for fear of reprisals.
The Tribunal has convicted eight defendants and acquitted one since it was established in 1995.