It is generally required to have two. They don't both have to be current; one can be current and the other can be successor, if you prefer. Sometimes you can function for a while with only one, but it isn't recommended. The trust would be orphaned, adrift at sea without a rudder, if anything were to happen to the one and only trustee. For that reason, most banks will not open an account for a trust unless it has two current trustees, OR one current trustee and one successor trustee.