Judge Lowell Goddard has opened the investigation into allegations involving public bodies or officials, including claims of an historical Westminster paedophile ring.
It won't have the power to convict anyone, or award compensation, but can name people who've abused children.
"We must put difficult questions to politicians, bishops and other faith leaders, headteachers, police officers and public officials of all kinds, and we will carry on putting those questions until we get the answers," said Judge Goddard.
The high court judge said "no one, no matter how powerful" they were would obstruct her investigation.
"No one will have immunity from scrutiny by virtue of their position", she added.
Goddard also said:
-The inquiry will focus on England and Wales and further afield if relevant
-All victims will be anonymised and not made to feel like they are on trial
-A victim advisory board has been appointed to provide specialist advice
-Immunity from prosecution will be offered to ex-public servants who testify but not if they admit taking part in child abuse
-The inquiry is expected to last five years but has "no cut off" and regular reports and recommendations on its findings will be published