In a court statement he read from a pre-written text, Breivik said the massacre had come from a place of goodness, not evil. His actions, he said, were aimed at deterring civil war.
"The most important thing today is that he gets to explain why he did what he did,” said Vibeke Hein Baera, a defense lawyer for Breivik.
On July 22 he set off a bomb in Norway’s capital, Oslo, killing eight people. He then went to a nearby island where members of the youth wing of the Labor Party were at summer camp. He shot dead 69 people; most of them were young campers.
Breivik has admitted the killings, but says the act is not criminal because his aim was to defend Norway.
His testimony will not be aired on television to avoid its use as propaganda for his extremist views. There has been concern in Norway the trial will give the killer publicity.
A survivor of the island shooting, Bjoern Magnus Jacobsen Ihler, was in the courtroom.
"It is difficult to sit there in the same room as the man who killed very many of my friends and who tried to kill me,"said Ihler. "But, at the same time, it is good to see him in this position because he is very reduced from where he was at the island. He can not harm me anymore and that is in many ways good to see.”
Many in Norway would prefer the trial not become a media circus.
Student Hildegunn Fallangbe also survived the shooting spree. She says she will not attend the court hearing because she does not want to take part in anything that will shine a spotlight on Breivik.
"He has expressed that parts of the reason he did it was to get attention, and attention to his manifesto," she said. And I do not really want to give him what he wants. To me we could just forget him.”
One of the lay judges in the trial was dismissed Tuesday for saying Breivik deserved the death penalty, a punishment that does not exist in Norway.
A major focus of the 10-week trial will be to determine if Breivik is clinically insane. If he is found to be so, he will be sent to a psychiatric institution indefinitely.
If he is found to be guilty and sane, he will face a maximum 21-year sentence that could be extended indefinitely if he is considered a continuing threat.