Laws governing wills vary from state to state and are usually located in a state’s statutes—in its estates code, for example. Generally, a will is a legal declaration of a person's intention or wish regarding the disposition of his property, the guardianship of his children, and the administration of his estate upon his death. It is said to be a means of transferring title to property. Any writing or declaration by which a person intends to dispose of his property or estate upon his death is a will, and if done as required by law, is entitled to probate as a will. A will vests no present interest in the property it intends to distribute—it is only effective upon the death of the person making the will (the testator). And a will is ambulatory—meaning the testator can change or revoke it during his lifetime.

A will may (1) direct how the testator's property should be disposed of upon his death; (2) direct how not to dispose of the testator's property, such as by expressly disinheriting a child or other heir; (3) revoke a prior will; and (4) appoint an executor of the testator's estate, and a guardian for the testator's children.

Some common types of wills include:

Holographic wills—a holographic will is a will that is written entirely in the testator's handwriting. A will intended by the testator as holographic will be enforced even though it contains words not in the handwriting of the testator, if such other words are not necessary to complete the will and do not affect its meaning. For example, an acknowledgment of a notary public and the notary public's signature are surplusage not necessary to complete the will and do not affect its meaning. A holographic will is not required to be attested by subscribing (signing) witnesses.

Attested wills—an attested will is a will that is attested to (declaring or swearing to the truth of) by two or more credible witnesses who are at least 14 years of age, and who sign their names to the will in their own handwriting in the testator's presence. An attested will can be handwritten by the testator, but usually is not.

Codicils—a codicil is a supplement to a previous will that adds to, modifies, or revokes one or more provisions of the earlier will.

In Illinois, the laws governing wills are outlined in the Illinois Compiled Statutes, specifically within the Probate Act of 1975. A will in Illinois is a legal document that expresses a person's wishes regarding the distribution of their property and the care of any minor children upon their death. To be valid, a will must generally be in writing, signed by the testator (the person making the will), and witnessed by at least two credible witnesses who are present at the same time and who also sign the will. Illinois does not recognize holographic wills, which are wills written entirely in the testator's handwriting without witness signatures, unless they are executed in compliance with the laws of a state that does recognize such wills. Attested wills, which are witnessed and signed by at least two credible witnesses, are the standard in Illinois. Additionally, a person may create a codicil, which is an amendment to an existing will, to make changes without drafting an entirely new document. The codicil must also be executed with the same formalities as a will. It's important to note that wills are ambulatory, meaning the testator can change or revoke them at any time before death, and they only take effect upon the testator's death.