In most states and for most estates of any significant value, a person's will goes through the process of probate to be enforced. This action ensures that all regulations are followed regarding the distribution of property and the transfer of title to inheritors. In probate, wills are closely examined to verify that they are valid. One or more of the witnesses who originally signed the will may be contacted to swear to the authenticity of the document. They can verify that the identities of all the signatories on the will are correct. They can also attest to the fact that the person making the will was mentally sound and not being forced or pressured to include or exclude anyone from the will.

During probate, wills that are invalid for any reason may be set aside by the court. In such cases, the "intestate" probate code of the state goes into effect and assets are handled according to standard procedures. In some circumstances, only a part of the will may be considered invalid. For example, if a beneficiary signed the will as a witness, he or she may be excluded from inheriting. This is one good reason to fully research the state rules to make sure a will isn't going to be thrown out during probate.