A caveat is an objection or challenge to a will that is brought about in order to have the will deemed invalid. In order to declare a caveat, the person doing so must have grounds such as claiming the testator was mentally incompetent. The person bringing the caveat must also be able to prove these grounds. Other grounds that are used for bringing caveats are that the will was created under duress or coercion by an undue influence. In order to prevent a caveat from being successful last wills and testaments should be prepare with the help of an estate planner and with witnesses that can attest to mental health and competency at the time the will was made.