The World Meeting of Families officially opens today.
Bells will ring this evening in Catholic cathedrals across Ireland's 26 dioceses to mark the start of the gathering.
Pope Francis will join the event on Saturday, and will celebrate its closing mass in the Phoenix Park in Dublin on Sunday.
Preparations have been overshadowed by revelations about the church's handling of clerical sex abuse.
Maeve Lewis from campaign group One in Four says the celebration will ring hollow for many abuse victims.
"I'm sure people who are attending the mass in the Park or the other events do not mean in any way to add to the suffering of the survivors," said Ms Lewis.
"But in many ways, that is what's happening because people feel that their suffering is just being ignored in the middle of this big international celebration."
Yesterday, Pope Francis
issued a letter to Catholics around the world condemning the "crime" of sexual abuse by priests and subsequent cover-ups, saying: "We showed no care for the little ones; we abandoned them."
- Digital Desk