An annulment is a lawsuit to have a court declare a marriage was invalid and the parties were never in fact married. The grounds for an annulment vary from state to state but typically include:

• the person seeking the annulment (the petitioner) was under age (18 years, for example) and did not have parental consent or a court order;

• the person seeking the annulment (the petitioner) was under the influence of drugs or alcohol and did not have the capacity to consent to the marriage;

• either party, for physical or mental reasons, was permanently impotent at the time of the marriage and the other party was not aware of the impotency;

• the other party used fraud, duress, or force to induce the petitioner to enter into the marriage;

• at the time of the marriage the petitioner did not have the mental capacity to consent to marriage or to understand the nature of the marriage ceremony because of a mental disease or defect;

• the other party was divorced from a third party within the 30-day period preceding the date of the marriage ceremony, and at the time of the marriage ceremony the petitioner did not know, and a reasonably prudent person would not have known, of the divorce; and

• the marriage ceremony took place before any waiting period (72 hours, for example) following issuance of the marriage license.

An annulment on any ground is often available only if the parties did not live together (cohabit) after the party seeking the annulment was no longer under the influence of drugs or alcohol, or learned of the facts that are the basis for the annulment sought. A marriage subject to annulment is often said to be a nullity, void, or void ab initio (void from the beginning).

The grounds for an annulment are usually found in a state’s statutes—often in the family code.

In Illinois, an annulment is legally referred to as a 'Declaration of Invalidity of Marriage.' The grounds for obtaining an annulment in Illinois are outlined in the Illinois Marriage and Dissolution of Marriage Act. These grounds include: one party being underage without proper consent (under 18 years old and lacking parental consent or a court order); either party being under the influence of drugs or alcohol and thus unable to consent; one party being unable to consummate the marriage due to physical or mental incapacity, with the incapacity unknown to the other party at the time of marriage; the use of fraud, duress, or force to obtain the marriage; one party lacking the mental capacity to consent due to mental disease or defect; one party having a living spouse at the time of the marriage, making the marriage bigamous; or the marriage license being improperly obtained or the marriage being conducted within the prohibited time frame after the issuance of the license. It is important to note that cohabitation after the discovery of the condition that provides the basis for annulment may bar the annulment in some cases. An annulled marriage is considered void or void ab initio, as if it never legally existed. To pursue an annulment, the petitioner should consult with an attorney to ensure proper legal procedures are followed.