A testamentary trust is a type of trust that you create, which will go into effect after you pass away. It is distinct from living trusts, which you can create and have go into effect during your lifetime.  You can create a testamentary trust within your will, which is why a will trust is another name for a testamentary trust. Testamentary trusts can be relatively easy to develop and can provide you with more control over an inheritance that you provide to someone, such as a minor child who you want to give an inheritance to.