The first public hearing in a long called for public inquiry into the Omagh bomb will start later.
The probe, led by chairman Lord Turnbull, is examining whether the atrocity could reasonably have been prevented by UK authorities.
Some 29 people, including a woman pregnant with twins, were killed in the dissident republican bomb attack which devastated the Co Tyrone town on August 15th, 1998.
Some of the bereaved families have called for decades for a public inquiry into alleged security failings.
Michael Gallagher, whose son Aiden was killed in the atrocity, said today’s hearing will be the first time since 1998 that all of the bereaved families, including those caught up in the blast from Spain, will come together.
Survivors are also expected to gather at the Strule Arts Centre in Omagh for the hearing which will include opening remarks from the chair and counsel to the chair Paul Greaney KC.
Commemorative and personal statements are set to be made during inquiry hearings next January.
The Irish Government earlier this month formally agreed to provide assistance to the inquiry.
