A joint will combines the wills of two testators into a single document. Though joint wills are allowed in Washington State1, we do not recommend making joint wills because they pose several problems while offering no significant advantages over separate wills.
When two testators have joined their wills into a single document, it raises the question of whether they intended to permanently bind themselves to the terms of the document. (Did they intend to make mutual wills?) Answering this question may require litigation after the first testator dies, litigation that could be avoided by making separate wills in the first place. Even if the testators do want to make mutual wills, they can do so in separate documents.
Joint wills should not be confused with mirror wills or mutual wills.