A "self-proving" will is a will that comes with something extra: a sworn statement from the witnesses who watched the will-maker sign the will. In most states, probate courts will accept this statement as evidence that the will is valid. This eliminates the need, after the will-maker has died, for the witnesses to come to court and testify about watching the will being signed.
If there's a dispute about the validity of a contract or a lease, the people whose signatures are on the document can take the stand and testify about whether or not their signature is genuine. But because a will doesn't have any legal effect until the person who signed it has died, that's not possible in probate court. There has to be another way to prove that a will is valid.
That's why witnesses are crucial to proving the validity of a will. After someone dies, and the will is submitted to the probate court, the court requires testimony from two adult witnesses that:
Witnesses can usually convey their knowledge to the court either in the form of live testimony or in sworn written statements (affidavits), signed in front of a notary public.
It can be troublesome (or impossible) to find the witnesses to a will years or decades later, and get them to either come to court or to sign affidavits describing how they watched the will being signed those many years ago.
That's where the self-proving affidavit comes in. If a sworn statement from the witnesses, made at the time the will is signed, is attached to the will, the witnesses won't have to come to court and testify.
In most states, the statement must be notarized—that is, signed in front of a notary public, who also signs the document and stamps an official seal on it. A few states, however, allow witnesses to sign a statement "under penalty of perjury." A notary doesn't have to be present, but the witnesses state that they are making a truthful statement—and that if they aren't, they realize they are committing the crime of perjury, or lying under oath.
A typical self-proving affidavit looks something like this:
We, _______ and_______, the witnesses, sign our names to this instrument, being first duly sworn, and do hereby declare to the undersigned authority that the testator signs and executes this instrument as the testator's will and that the testator signs it willingly (or willingly directs another to sign for the testator), and that each of us, in the presence and hearing of the testator, hereby signs this will as witness to the testator's signing, and that to the best of our knowledge the testator is 18 years of age or older, of sound mind, and under no constraint or undue influence.
("Testator" is legal term that refers to the will-maker.) Typically, witnesses sign the self-proving affidavit at the same time that they sign the will itself, immediately after watching the will-maker sign it. But many courts will accept an affidavit that was signed later.
Not every state allows for self-proving wills. In the District of Columbia and Ohio, the self-proving option is not available.
In addition, in California, Illinois, Indiana, Maryland, and Nevada, it's not necessary to take extra steps to make a will self-proving. Simply having the witnesses sign the will under oath is enough to admit the will into probate.