The scene of devastation after a bomb explodes in Omagh on Saturday, August 15, 1998 killing 29 people, including two unborn twins
Inquiry chairman Lord Alan Turnbull is expected to set out its direction during a day of proceedings in the town at the Strule Arts Centre.
It is described as a preliminary session to deal with procedural issues.
No witnesses will be called or evidence heard until next year.
Twenty-nine people, including a woman expecting twins, were murdered in the Real IRA attack on Saturday, August 15, 1998.
The inquiry will examine whether steps could have been taken to prevent the bombing, which was the the biggest single atrocity of the Troubles.
It was established last year, following a long legal battle by some victims’ families.
The inquiry will also look at the issue of intelligence sharing between RUC Special Branch, MI5 and An Garda Siochana before and after the atrocity.
Michael Gallagher, whose son Aiden was one of those killed in the bombing, said the inquiry has been an “unbelievably long time coming” but said he hopes it will be ”the beginning of the end”.
“As a bereaved parent, I will be happy in the knowledge that I have done everything that I could to try and bring justice and truth,” he told BBC Radio Foyle’s North West Today programme.
Mr Gallagher said he expects the inquiry to last a couple of years due to the sheer amount of material to wade through and the number of witnesses to interview.
“We are just looking forward to the process starting and then we’ll know better how it’s going to work,” he said.
“It’ll just be interesting to see, as we move through this inquiry, what we discover and what will end up.
“We hold out the hope for truth -whether we get justice or not is another question.”
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