A public inquiry into the murders of 29 people in the Omagh bombing in 1998 is under way in the Co Tyrone town.
Families of those who died will begin outlining their personal stories and the impact of their loss.
The inquiry was established to examine whether the bomb attack in Omagh by the dissident republican group the Real IRA could have been prevented.
More than 200 were injured in the huge blast, many of them seriously.
The inquiry chairperson Alan Turnball has made it clear that he wants to hear the stories of those killed and injured, and the many others impacted by a bombing that caused the biggest single loss of life in the history of Northern Ireland's Troubles.
Relatives of each of those who were killed will have the opportunity to make personal testimonies about them, the kind of people they were and the impact of their loss.
Some families may include photographs and home video of their loved ones.
Those commemorative hearings will last for two weeks, followed by a week of statements by survivors of the atrocity, then a week of the stories of members the emergency services who dealt with its aftermath.
All of the statements will be live streamed and can be viewed by members of the public.
The evidential hearings are expected to be held before the summer and are expected to include contributions from the Irish government, are expected to be held before the summer.
The Real IRA bomb was made in the Republic and some of those involved lived there.
The Irish Government, which has been criticised by many of the relatives for not establishing its own inquiry, has said it will do all in its power to help the UK hearing.
