Right-wing extremist Anders Behring Breivik pleaded not guilty to charges he committed "acts of terror" when he massacred 77 people in twin attacks in Norway last July.
"I acknowledge the acts, but not criminal guilt and I claim self-defence," he told the court on the first day of his 10-week trial.
The judge then entered the plea as "not guilty."
His plea came after prosecutor Inga Bejer Engh spent over an hour reading the charges against him, including "acts of terror," and listing each of his 77 victims and and how they died.
Breivik, 33, has described his actions as "cruel but necessary" and claims he acted alone and in self-defence against those he considered to be "state traitors" for opening Norway up to multiculturalism and allowing the "Muslim invasion" of Europe
Anders Behring Breivik, dressed in a dark suit, smiled as a guard removed his handcuffs in the crowded court room. The 33-year-old then flashed a closed-fist salute, before shaking hands with prosecutors and court officials.
"I don't recognize Norwegian courts because you get your mandate from the Norwegian political parties who support multiculturalism," Breivik said in his first comments to the court.
Breivik also said he doesn't recognize the authority of Judge Wenche Elisabeth Arntzen, because he said she is friends with the sister of former Norwegian Prime Minister and Labor Party leader Gro Harlem Brundtland.
The anti-Muslim militant described himself as a writer, currently working from prison, when asked by the judge for his employment status.
After opening statements Monday, Breivik is set to testify for five days, explaining why he set off a bomb in downtown Oslo, killing eight, and then shot to death 69 people, mostly teenagers, at a Labor Party youth camp on Utoya island, outside the Norwegian capital.
Breivik has admitted to the attacks, claiming they were necessary to protect Norway from being taken over by Muslims, but has rejected criminal guilt. He is facing terrorism and premeditated murder charges.
The key issue to be resolved during the 10-week trial is the state of Breivik's mental health, which will decide whether he is sent to prison or to psychiatric care.
On July 22, Breivik killed eight people when he set off a bomb in a van parked at the foot of government buildings in Oslo housing the offices of Labour prime minister Jens Stoltenberg, who was not present at the time.
He then travelled to Utoeya island outside Oslo where, dressed as a police officer, he spent more than an hour methodically shooting at hundreds of people attending a Labour Party youth summer camp.
The shooting spree left 69 people dead, most of them teenagers trapped on the small heart-shaped island surrounded by icy waters, and is the deadliest massacre ever committed by a sole gunman.
with AP/AFP inputs