The Irish Justice Minister and Lord Mayor of Dublin will join bereaved families today to remember those killed in the Dublin and Monaghan bombings.
A total of 33 people - and an unborn child - were killed on May 17, 1974 after the UVF planted a series of bombs.
Three car bombs exploded in Dublin city centre, and a fourth bomb caused devastation in the centre of Monaghan town.
Margaret Urwin, from Justice for the Forgotten, said the family's campaign to find out the truth of what happened goes on.
The bombs are among the investigation being carried out by the Police Ombudsman in Belfast into the Glenanne gang, a group of loyalist terrorists, RUC and UDR officers who worked together.
Mrs Urwin said for the families of those killed in the bombings, marking the anniversary each year means a great deal. However, she said many of the relatives are dying without ever finding out the truth.