2 things differentiate a Testamentary Trust and a Living Trust: who builds the trust and when is the trust built. A Testamentary Trust is really a Will. A Will that contains instructions to build a trust if one is needed. For example, the Will could say if a beneficiary (one who is to inherit under the Will) is not X age (maybe 26 yo) then a trust needs to be built at the end of the probate process so the inheritance can be put in a trust and NOT be given directly to the person. Built after you