Double wills refer to mutual or reciprocal wills where two individuals create very similar wills with the intention of each individual receiving the assets of the other should they die first. The nature of double wills depends on what type of double will is being referred to.
Mutual wills are double wills where the two individuals agree that the survivor cannot change their will after the other dies. The goal of this is so that children, friends, or other inheritors specified in the document cannot be changed after one dies, binding both individuals to the wills. The wills can be changed before one of the two individuals die with adequate notice to the other party. If one tries to create a mutual will, some states require an explicit agreement that the wills were meant to be irrevocable after the death of one of the parties, but in others, an oral agreement may suffice. The surviving individual cannot attempt to go around this limitation by gifting away assets allocated in the will inter vivos either.
Reciprocal wills are not mutual wills because should one of the individuals die, the other can still change their will. The main point to reciprocal wills is that each spouse agrees that the other receives the entirety of their assets upon death.
[Last updated in January of 2022 by the Wex Definitions Team]