The Historical Institutional Abuse (HIA) inquiry is due to begin investigating claims of child abuse in residential homes and borstals today.
The Statutory Inquiry part of the investigation will cover allegations made during a period of 73 years, from 1922 to 1995. Over 400 people contacted the inquiry with claims of neglect and sexual, physical and psychological abuse.
The public hearings will take place in Banbridge, County Down, with 300 people due to testify. They will be offered anonymity and the opening address will be given by chairman and retired judge Sir Anthony Hart.
The institutions and social care trusts will also give evidence in this part of the investigation, as well as testimonies from the government.
This stage of the investigation is due to take around 18 months and 13 children's homes and juvenile justic centres are currently under inquiry.
The institutions were run by the state, the Catholic church or by voluntary organisations.
Since October 2012, evidence has been recorded from approximately 263 alleged victims, in private sessions to the inquiry's Acknowledgement Forum.
The HIA was set up by Northern Ireland's first and deputy first ministers on 31st May 2012.
It is the largest public inquiry into child abuse in the UK.
When it was launched, Jonathan Bell, junior minister, said it would "examine if the institutions or the state failed in their duties towards children under 18 in their residential care and if failings were systemic."
Jennifer McCann, junior minister serving with Bell, added: "Victims were robbed of their dignity, their self respect and their childhoods.
"The Inquiry gives victims and survivors the opportunity to talk about their experiences and for their suffering to be acknowledged.
"It will make recommendations about an apology, a memorial and the requirement or desirability for redress by institutions and/or the Executive to meet the particular needs of victims."
The Survivors and Victims of Institutional Abuse support group (SAVIA) had previously lobbied for the inquiry to commence.
Of the 434 alleged victims due to testify, a third have moved out of Northern Ireland and now reside elsewhere in Great Britain, the Republic of Ireland, Australia and other countries.
The majority remain in Northern Ireland.
For the first three days, a general overview of the proceedings and the issues to be addressed will take place. The first stage of the inquiry will focus on allegations made against two Londonderry children's homes run by the Catholic church.
The Sisters of Nazareth order of nuns ran the two homes, Nazareth House Children's Home and St Joseph's Home.