An Irrevocable Trust cannot be altered, changed, modified or revoked after its creation (absent extreme extenuating circumstances). Once a Grantor transfers property to an Irrevocable Trust, the Grantor can no longer take the property back from the Trust.
Though, by design, an Irrevocable Trust cannot be changed, there are certain exceptions that allow Beneficiaries or the Trustee to modify the Trust. One example is when an estate plan includes a Trust Protector who can look over the trust details to make changes. In addition, if the assets in a Trust are sold, the Trust is terminated.
Irrevocable Trusts come in two forms: Living Irrevocable Trusts and Testamentary Irrevocable Trusts. A Revocable Trust generally becomes an Irrevocable Trust after the Grantor dies.