The inquiry resumed hearings on Monday, focusing on the child migration programme.
Over the next three weeks evidence will be heard from 50 people who are now living in Australia.
A number of witnesses are scheduled to give their evidence in person but most will give evidence by video-link.
Documentation examined by the Inquiry has revealed that approximately 140 young children from Northern Ireland who were in the care of voluntary institutions, or state bodies, were sent to Australia as child migrants between 1922 and 1995.
The Sisters of Nazareth order of Catholic nuns was responsible for the removal of 111 child migrants aged as young as five, some of whom faced sexual and physical violence after arrival.
Some were orphans, but in some cases they were not and were told they had no living relatives.
Reasons for transport included boosting 'Catholicisation' in the establishing colonies, propping up the number of white people in the Empire and saving money by clearing spaces in overcrowded workhouses, Christine Smith QC, told the inquiry.
"Therefore the fare to Australia would be money well spent," she explained.
"It was reckoned that it would be cheaper to send a child abroad than to keep it for several years in a workhouse."
A statement read from one witness, who has since died, said: "My life in institutions has had a profound impact on me. I have always wondered what it would have been like to have had a family, a mother and father and brothers and sisters.
"I never got the chance to find out because I was sent to Australia.
"It is hard to understand why they did it, I know the theory, to populate Australia."
He added: "I was treated like an object, taken from one place to another. I found it very hard to show affection to my children when they were young.
"I have a nightmare every night of my life; I relive my past."
The inquiry, which is chaired by retired High Court judge Sir Anthony Hart, is limited to what happened to children in institutions in Northern Ireland and does not have the power to investigate what befell migrants in Australian institutions.
However, Sir Anthony added: "That does not mean that their accounts of their experiences in Australia will be swept under the carpet. I want to assure them that will not be the case."
Statements will be furnished to the Royal Commission into Institutional Responses to Child Sexual Abuse in Australia.
The Historical Institutional Abuse Inquiry was formally established in January 2013 by the Northern Ireland Executive. It has a remit to investigate child abuse which occurred in residential institutions in Northern Ireland over a 73-year period up to 1995.
In total, the Inquiry is expected to hear from more than 300 witnesses during the course of the public evidence sessions.
Hearings and all investigative work is required to be completed by mid-summer 2015, with a report to be submitted to the Northern Ireland Executive by 18 January 2016 - although Sir Anthony Hart has asked the First and deputy First Ministers for an extension of one year.
To date, 523 individuals have made a formal application to speak to the Inquiry or its Acknowledgement Forum.
People currently living in Northern Ireland make up 330 of those applications.
There has also been 92 applications from Great Britain, 26 from the Republic of Ireland and 10 from other countries.
The Inquiry's Acknowledgement Forum has now met with 416 applicants.
A total of 13 institutions in Northern Ireland are currently under investigation by the Inquiry in relation to allegations of historical institutional abuse and/or neglect.
The inquiry has heard a litany of allegations from former residents at Londonderry homes run by Sisters of Nazareth nuns, including that children were made to eat their own vomit and bathe in disinfectant.
They claimed they were beaten for bedwetting and had soiled sheets placed on their heads to humiliate them, witnesses told public hearings earlier this year.