Around 800 people are expected to gather in Utøya, the island where Breivik shot 69 people at a Workers' Youth League (AUF) camp three years ago.
The event is organized by the AUF and will take place during this year's annual summer camp.
Members of the AUF will release 69 balloons to commemorate the deceased.
Bergen are among those going to Utøya on Friday. Photo: Fredrik Varfjell / NTB Scanpix.