A ceremony will be held in Dublin today to mark the 38th anniversary of the Dublin and Monaghan bombings, which claimed 34 lives.
The Justice For The Forgotten group, which was formed in 1996 to campaign for truth and justice for the victims of the bombings, will hold a wreath-laying ceremony at the memorial on Talbot Street, beside Connolly Station.
Archbishop of Dublin Dr Diarmuid Martin will celebrate a commemorative mass at St Mary's Pro-Cathedral at 12.45pm.
33 people, including a pregnant woman, were killed and almost 300 were wounded in a series of car bombings on 17 May 1974 - the highest number of casualties in any one day during The Troubles.
No warnings were given before the bombs exploded.
Three exploded in Dublin during rush hour, killing 26 people and an unborn child, and one exploded in Monaghan an hour and a half later, killing seven people.
Most of the victims were young women, although the ages of the dead ranged from five months to 80 years.
The Barron Report into the bombings, which was published in 2003, found that the attacks were carried out by loyalist paramilitaries.
Nobody has ever been charged with the attacks.