Anders Breivik attacked a summer youth camp organized by the governing Labour party on the island of Utoeya, after setting off a car bomb in the capital.
He gave a closed-fist salute, and said he did not recognize the court because it was dependent on political parties who supported multiculturalism.
Anders Breivik has confessed to the killings, but denies criminal responsibility.
If the court decides he is criminally insane, he will be committed to psychiatric care; if he is judged to be mentally stable, he will be jailed.
In the latter case, he faces a sentence of 21 years, which could be extended to keep him behind bars for the rest of his life.
Dressed in a dark suit, Anders Breivik smiled as he entered the courtroom and a guard removed his handcuffs. He then gave a closed-fist salute.
Anders Breivik later told the lead judge: “I do not recognize the Norwegian courts. You have received your mandate from political parties which support multiculturalism. I do not acknowledge the authority of the court.”
The judge noted the objection, which Anders Breivik’s lawyer said was not an official one, and said the lawyer could follow up on the matter in his opening arguments.
The prosecutor then read the names of all the victims of the attacks last July, describing in detail how each person was killed or injured.
Anders Breivik showed no emotion, looking down at a folder on the table in front of him.
During the 10-week trial, prosecutors will paint a detailed picture of how one man planned and then carried out mass murder.
Anders Breivik has already confessed to the attacks – first the car bombing outside government buildings in Oslo which killed eight people, and then the shooting spree at a political youth camp on Utoeya.
He is expected to plead not guilty, arguing that the Labour party was a “legitimate target” because it supports immigration and multiculturalism – policies he says will bring about a Muslim takeover of Europe.
With Anders Breivik not expected to express any remorse for his actions, his trial promises to be an ordeal for the families of those killed and for those who survived the attacks.
Jorid Nordmelan, a survivor of the Utoeya massacre, said she would be in court to hear Anders Breivik testify.
“It’s a historical date for Norwegians,” she said.
“We never had a trial like this, so we don’t know what’s going to happen.
“Prosecutors told me they were going to make the opening statements awful, so that people can just feel what he did right there.”
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