In brief: You may want to specifically exclude someone from your will that might have been expecting to receive a share of your estate. In some cases they may have a claim on your estate even though you excluded them in the will.
More details below..
In certain circumstances, if you have excluded close family members from your Will they may make a claim on your estate. In England and Wales the Inheritance (Provision for Family and Dependants) Act 1975 ensures that certain people who are dependant upon you prior to your death, are adequately provided for after your death.
The types of person who may make a claim are:
In Scotland the surviving spouse/civil partner or children can, if they wish, make a claim on your estate. Such persons can apply to the Court for provision to be made. If you wish to exclude someone in these categories from your Will you should seek specific legal advice.
Next: Alterations to a will.
See Legal Wills - a range of standard Wills for use in England, Wales and Scotland. If you want to modify a will see our range of Codicils.