Memorial services were held, from those in individual homes to churches to a service in the Oslo Cathedral.
Prime Minister Erna Solberg addressed a memorial service attended by survivors and relatives of the victims, political leaders and Norway's Royal family.
"It hurts to think back to that dark day in July ten years ago. Today, we mourn together. Today, we remember the 77 that never came home," Solberg said.
The memorial was held in central Oslo outside what was once the prime minister's office. People also expressed their sorrow by leaving red roses at cathedral and in public places.
Eight of the victims died when a car bomb was detonated outside a tower block housing the offices of then Prime Minister Jens Stoltenberg. Less than two hours later, a lone gunman attacked a summer camp organized by the ruling Norwegian Labour Party, killing 69 people and injuring more than 100 others.
Norwegian Bishop Erik Varden spoke of the "grief and perplexity" of Norwegians. The attack was the deadliest violence in the country since the Second World War.
Ten years, on, “the nation is still in grief, and still struggles to understand how something as brutal as that act could happen in a nation that is peaceful, and that prides itself on being peaceful,” said Varden. He added, “So we’re united in grief and perplexity and also in indignation that such a thing should have happened here.”
The victims came from all parts of the country and memorial services were also held across Norway, with people also laying down flowers in other cities.
A group of survivors have set up a Twitter account @aldriglemme (Never forget) to re-post tweets about the attack as they appeared 10 years ago.