Washington Letters Testamentary With Oath are legal documents that appoint an executor of an estate in the state of Washington. They are used to prove the executor's authority to handle the deceased’s assets and liabilities. The letters are granted by the court upon application and are issued by the court clerk or Probate Registrar. There are two types of Washington Letters Testamentary with Oath. The first is a standard Letters Testamentary with Oath, which is granted to an executor who has been named in a will. The second type is referred to as Letters Testamentary with Oath of Substituted Executor, which is granted when the will names an executor who is unable or unwilling to serve. Both types of letters require an Oath of Executor, which is taken by the executor before they can access the deceased's assets.