A last will and testament, commonly referred to as a will, is the legal document executed by someone which directs how that person wishes his or her assets to be distributed when he or she dies. The individual who creates and executes a will is known as the "testator." Along with the testator, most jurisdictions require that a will be witnessed by at least two individuals. The requirements regarding who may witness a will, as well as other formalities required to make a will valid, will vary by jurisdiction. Within the United States, laws regarding who may witness a will vary by state; however, in most cases, a witness must be over the age of 18, of sound mind, and, in some cases, may not be a beneficiary under the will.
The requirement that a will be witnessed has been around for as long as wills have existed. The reason for requiring that someone witness a will is to have a manner to authenticate the will in the event that there is a question as to whether the testator actually signed the will or the state of mind of the testator at the time of signing. In the digital age, with the advent of video wills and other mechanisms for assuring that the will is valid, the need for witnesses is becoming archaic; however, most jurisdictions retain the requirement for written wills unless the will is a holographic, or handwritten, will.
Within the United States, state law determines what constitutes a valid will. At a bare minimum, most states require that the testator to a will be over the age of 18 and of sound mind and that the will have at least one, and generally two, witnesses. A person who is legally allowed to witness a will must have reached the age of majority — 18 in most states — and also be of sound mind in order to understand what he or she is witnessing.
In addition to the age and mental faculty requirements, most jurisdictions also preclude beneficiaries from being a witness to a will. A beneficiary is someone who is specifically mentioned in the will as receiving a bequest. An heir, on the other hand, is someone who would inherit under the laws of intestate succession, or in the absence of a will. A beneficiary may also be an heir, but does not have to be.
The theory behind precluding beneficiaries from witnessing a will is to prevent any conflict of interest on the part of the witness. If there is a question as to the validity of the will, or the state of mind of the testator when the will was executed, then courts prefer to have a disinterested party to give testimony regarding the signing of the will. Clearly, beneficiaries cannot be considered a disinterested parties, which is why most jurisdictions do not allow them to witness a will.