An irrevocable trust is a trust that cannot be amended, modified, or terminated by the grantor, settlor, or trustor (person who created the trust) after it is created—at least not without the permission of the beneficiary or beneficiaries.

Irrevocable trusts generally offer tax benefits that revocable trusts do not. This is primarily because the grantor, settlor, or trustor who creates an irrevocable trust permanently transfers (gifts) all right of ownership of the assets to the trust and its beneficiaries.

Laws vary from state to state but a trust is usually irrevocable unless the grantor, settlor, or trustor specifies otherwise in the trust agreement.

In Montana, an irrevocable trust is a type of trust that, once established, cannot be altered, changed, or terminated by the person who created it, known as the grantor, settlor, or trustor, without the consent of the trust's beneficiaries. The main characteristic of an irrevocable trust is the transfer of ownership of assets from the grantor to the trust, which is managed for the benefit of the beneficiaries. This transfer is considered permanent and results in the grantor relinquishing control over the assets, which can lead to potential tax advantages. These tax benefits are often related to estate taxes and gift taxes, as the assets in the trust are no longer part of the grantor's taxable estate. In Montana, as in other states, the terms of whether a trust is revocable or irrevocable are typically outlined in the trust agreement. If the trust document does not explicitly state that the trust is revocable, it is generally presumed to be irrevocable. Montana statutes and case law would govern specific aspects of irrevocable trusts, including their creation, administration, and the rights of beneficiaries.