Invalidated by Statute
A will that does not meet statutory requirements, or the criteria for will validity as set forth in state laws, may not be used no matter how old the document is. The statutory requirements vary by state. Common requirements are the signature of the testator -- the person the will belongs to -- or a representative asked by the testator to sign the document and the signature of witnesses. If all of the witnesses required to sign the will under law die before the testator, the will may not be valid for probate, the legal proceeding used to settle the estate of a deceased person with a will. Some states require an affidavit from at least one living witness to the will for probate.
Revoked by Testator
The testator may draft a new will for a variety of reasons. A life-changing event, like the death of a spouse, may impact an older will. An heir who is no longer part of the family may need to be removed as a beneficiary under a prior will. A new will intended to revoke a previous will must contain language indicating its purpose. The testator does not have to file an entirely new will to change a provision in an older will. A codicil, or document used to alter a will provision, may be used instead.
Operation of Law
A will may be revoked under state law after the testator has died. Some situations automatically invalidate a will's provisions. A deceased person who left his estate to a legal spouse at the time of the will's execution may have the will revoked by law if he subsequently divorced. A will leaving everything to a deceased heir may be revoked by law if the document did not include a provision for the death of the heir. In some states, a deceased heir's children may still inherit under a will even if no provision is made.
A physical act by an heir or beneficiary under a will may invalidate all or part of the document in some states. The murder of the testator at the hand of a beneficiary is legal cause to void the will itself or the provision granting the beneficiary a share. The documented attempt of a beneficiary to defraud or steal from the testator may result in the invalidation of a will provision or the document in its entirety.