The Independent Inquiry into Child Sexual Abuse in England and Waleshas begun its first hearing, two and a half years after it first began.
The inquiry has been dogged by controversy since being set up in 2014 and is now on its fourth chairwoman and has cost £23.6 million to date.
The IICSA was set up after the death of Jimmy Savile in 2011 when hundreds of people came forward to say he had abused them as children.
The spotlight then fell on sexual assaults carried out in schools, children's homes and at NHS sites, as well as on claims of past failures by police and prosecutors to properly investigate allegations.
The first hearing will begin with the child migration programme, which were large-scale schemes in which 130,000 children from poor families or in the care system were sent to parts of the British Empire between 1920 and 1974, by religious institutions and charities with the aim of giving them better lives.
However, many suffered physical and sexual abuse in homes and so-called farm schools run by religious orders and charities.
Children and their parents were often not consulted on the moves, and siblings were frequently separated.
Most of the children were sent to Australia, Canada, New Zealand, and what was then Southern Rhodesia (modern-day Zimbabwe).
The inquiry will hear from a number of former child migrants who have alleged they suffered sexual abuse in relation to their migration.
It is thought that the inquiry will be told that the scale of sexual abuse the children suffered was much wider than previously thought.
In 2009, the Australian government apologised for the cruelty shown to the child migrants, while Britain also apologised in 2010.
A £6 million family restoration fund was set up to allow the migrants to travel to the UK and ministers are now considering extending it.
The inquiry is currently on its fourth chair, Professor Alexis Jay, following the departures of Baroness Butler-Sloss who resigned after just one week due to concerns over her links to the establishment - namely her late brother, Sir Michael Havers, who was attorney general in the 1980s.
Fiona Woolf resigned after only two months, after discolosing she had been to five dinners with the late Lord Brittan, who was one of those facing accusations at the time. All accusations against Lord Brittan have since been dropped.
Dame Lowell Goddard held the position for 18 months, but quit in August 2016 due to "compounding difficulties" and her family life.
In November, one of the largest groups representing abuse victims' in the inquiry pulled out of the process.
The Shirley Oaks Survivors Association said the inquiry had become a "stage-managed event" that enabled "the guilty to wash their dirty hands, whilst the establishment pats itself on the back", and that it had lost confidence in the leadership.
Despite calls for her to quit following the resignations, Prof Jay has vowed to continue in the job.
The hearings will take place at the International Dispute Resolution Centre in London, with the first phase concerning Australia expected to last 10 days.
Following the child migration hearings, the inquiry will go on to investigate claims against councils, religious organisations, the armed forces, and public and private institutions.