A testamentary trust is a trust that is established in accordance with the instructions contained in a last will and testament. A trust is a fiduciary relationship that allows a trustee, who is a third party, to manage assets on behalf of the beneficiaries of the trust.

A person's will may include instructions to establish a testamentary trust so that the trustee can distribute the person's assets to the beneficiaries outlined in the will. However, a testamentary trust is not created until after the person has passed away. Also, a will could have more than one testamentary trust.