For a Last Will and Testament to be considered valid, certain requirements must be met, including:The decedent needs to be a legal adult (meaning they are above the age of majority in their jurisdiction) and of sound mind (meaning they have the mental capacity to sign legal documents for themselves)
The testator was not pressured into creating their Last Will or into gifting assets to a certain beneficiary (a concept known as undue influence)
The Last Will has been properly executed, which means it has been signed and witnessed
If a Last Will is not completed properly, it may be considered invalid. In some instances, however, even a valid Last Will can be contested (i.e. disputed in court) if someone (like a beneficiary, executor, unnamed heir, etc.) believes the Last Will wasn't written properly or that the deceased was pressured into creating it.