Right-wing extremist Anders Behring Breivik sets off a bomb near the government building in Oslo, killing eight people and injuring dozens of others. He then goes on a more than hour-long shooting rampage on the nearby island of Utøya, where the ruling Labour Party's youth wing is hosting a summer camp.
He kills 69 people on the island, most of them teenagers, before he is arrested.
Breivik appears before a judge for the first time and is remanded in custody.
Norway observes a minute of silence and between 150,000 and 200,000 people march in Oslo carrying roses, the symbol of the Labour Party, to commemorate the victims.
The government creates a commission tasked with determining what lessons to draw from the carnage. It is set to present its conclusions on August 13th 2012.
August 19 and 20
Survivors of the Utøya massacre and loved ones of those who died there are for the first time permitted to visit the island.
Norway holds an emotional commemoration for the victims.
The populist anti-immigration Progress Party, of which Breivik had once been a member, suffers a severe setback in Norway's first elections -- local -- since the massacre.
Two court-appointed psychiatric experts conclude that Breivik is psychotic, suffering from "paranoid schizophrenia", which means he should be locked up in a psychiatric institution rather than prison.
Amid continued controversy over the results of the first evaluation, the Oslo district court orders a new psychiatric examination of Breivik.
Breivik is placed under all but constant observation by psychiatric experts over a period of three weeks at the Ila prison, near Oslo.
Norwegian prosecutors formally charge Breivik with committing "acts of terror".
Norwegian police apologize for failing to arrest Breivik sooner.
The second team of court-appointed psychiatric experts says it has seen no signs that Breivik is psychotic and concludes he is criminally sane. But this assessment is not approved by the forensic psychiatric commission.
Breivik's trial opens with him pleading not guilty.
Some 40,000 Norwegians march in Oslo, carrying roses and singing a children's song hated by Breivik.
The brother of a young Iraqi Kurd killed on Utøya throws a shoe at Breivik in court, but misses him.
The prosecution says Breivik's sanity has not been proven beyond a reasonable doubt and call for him to be locked up in a psychiatric ward instead of prison.
On the last day of his trial, Breivik insists his attacks were justified and demands his acquittal, while his lawyers argue he is sane and call for him to receive the "mildest possible" prison term.
Ceremonies are held to commemorate the first anniversary of the attacks.
An independent commission submits a scathing review of the authorities' response to the attacks, saying they could have prevented the Oslo bombing and arrested Breivik sooner as he carried out his shooting spree on Utøya.
The head of Norway's police resigns after the damning report on the authorities' handling of the attacks.
The Oslo district court finds Breivik sane and sentences him to 21 years in prison, to be extended if he is still considered a threat to society after that.