Some of the best fictional drama comes from families battling over an inheritance. It's easy to set the scene: A rich person with a terminal illness meets someone who provides some combination of care and romance; they decide to marry; and the dying person leaves the entire estate to the new spouse. Or here's another one: An opportunistic child persuades a dying parent to make a last-minute change to a will, disinheriting the parent's other children. After the person dies, fireworks are sure to ensue.

In real life, will contests are somewhat more rare, but they still occur from time to time. Howard Hughes, whose aviation and engineering businesses now live on as part of Boeing (NYSE:BA) and Raytheon (NYSE:RTN), was involved in a will contest that lasted for years after his death. More recently, Anna Nicole Smith continues to battle the children of her late husband, J. Howard Marshall, and News Corp.'s (NYSE:NWS) Rupert Murdoch is facing friction from family members -- even while he's still alive -- that may well eventually escalate to a will contest among children and current and former spouses. Under certain circumstances, people can challenge another person's will, and some such challenges hold up to the scrutiny of a court. If you believe you've been treated unfairly in someone else's will, or if you're trying to draft a will in a family situation in which there's a risk of someone challenging it, here's what you need to know about will contests.

Who can challenge a will
Not everyone is allowed to contest another person's will. To have standing to challenge a will, you must demonstrate that you have a legitimate interest in the person's estate. There are two common ways to establish your estate interest. First, if you were named as an heir in a previous will that the challenged will replaced, you can contest the will. Second, you can generally contest a will if you would receive money from the estate under the laws of intestate succession, which apply when a person leaves no valid will. In practical terms, what this means is that the deceased person's spouse and children are usually entitled to file a will contest, and other relatives, friends, or unrelated parties will also have standing to contest a will.

Perhaps a simpler way of thinking about will contests is that to contest a will, you must stand to gain something if you win. This prevents people from having to worry about unrelated people contesting a will just to be a nuisance to the deceased person's family during the will probate process.

Grounds for contesting a will
There are several valid reasons to contest a will. To create a valid will, a person must have the mental capacity to understand what he or she is doing in a will. However, the definition of mental capacity used for will contests is different from what is used in other contests. For instance, in some cases, someone who has been declared incompetent to manage everyday personal financial affairs can still have the capacity to create a valid will. Perfect health is clearly not necessary. The primary concern is that a person creating a will must have a basic understanding of his or her estate assets and who his or her close relatives are.

Another basis for a will contest involves undue influence over the person making the will. This commonly arises in situations involving a family member who was disinherited in favor of another family member or an unrelated party. If the person making the will was so strongly coerced to make a change to the will that the person no longer had free will to do otherwise, then a court is likely to find undue influence. As an extreme example, if you needed medicine to survive, and someone threatened to take your medicine away unless you signed a new will leaving everything to that person, there would be clear undue influence that could nullify the new will.

In addition, there are some technical reasons for contesting a will. Most states require a will to be signed by the person making it in the presence of a certain number of witnesses. If the requirements of state law aren't met, then a will may be declared invalid.

Making a will contest
Contesting a will is a legal action brought against the executor of the deceased person's estate. In many cases, the executor will file the will and other required documents with a local court that specializes in probate matters. Those who wish to contest the will must do so within a period specified by state law. The mechanics of a will contest can vary widely from state to state.

The burden of producing evidence is generally on the person contesting the will. If the contesting person produces enough evidence supporting the will contest, however, the executor of the estate may have to produce contrary evidence to support the final will.

Avoiding contested wills
Because will-contest litigation can be costly and emotionally painful to surviving family members, the best way to avoid will contests is to draft your will carefully, taking into account potential future conflict. You should let your estate-planning attorney know whether particular family members are likely to cause problems in response to the provisions of your will; your attorney will be able to suggest different strategies for trying to resolve these problems in advance.

Some attorneys recommend including a clause in your will that says that people who contest the will forfeit any inheritance from the estate if they lose. Clearly, this works only for people who would receive something under the will; if someone is already disinherited by the will, they have nothing to lose from making a will contest. Furthermore, courts in many jurisdictions dislike these clauses and sometimes choose not to enforce them, even when they might otherwise apply.

Although will contests are sometimes necessary to correct injustices, they are rarely successful and always demand a great deal of personal and legal effort. The difficulty of successfully challenging a will makes it clear that the best time to resolve disagreements among family members is while everyone is still around to talk through them.

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Fool contributor Dan Caplinger has seen the dark side of family inheritance battles but was lucky enough to avoid it with his own parents. He doesn't own shares of any of the companies mentioned in this article. The Fool's disclosure policy gives you information without a contest.