The new status will enable the charity to have access to all relevant documentation and can help guide the inquiry.
Core Participant status can be given to an individual, organisation or institution that has a specific interest in the work of the Inquiry.
The new investigation will review the current child protection policies and procedures in religious institutions in England and Wales, including non-conformist Christian denominations and Jehovah's Witnesses.
Those within the Islamic, Jewish, Sikh, Hindu and Buddhist faiths will also be reviewed.
Thirtyone:eight will be represented throughout the investigation by its CEO, Justin Humphreys.
Humphreys said in a statement: "We feel immensely privileged to have been given this opportunity to work alongside the Inquiry in this way.
"There are few organisations that have worked so closely with faith-based organisations for as long as we have to support best practice in safeguarding.
"This has helped us to gain unrivalled knowledge, understanding and expertise that is now clearly important to the Inquiry as they explore the extent to which children have been and are protected in this wider range of organisations and settings.
"Today's decision is recognition of this and we accept the responsibility this carries with humility and a desire to see further strengthening of safeguarding across the faith sector."
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