Annulments are similar to divorces in that each makes a determination regarding marital status. However, there is a vital difference between the two. While a divorce ends an existing, valid marriage, an annulment declares that what was thought to be a valid marriage never really existed.In Illinois, an annulment action is referred to as a declaration of invalidity of marriage and since there are much stricter requirements, it is very difficult to declare a marriage invalid. In order for a court to declare an Illinois marriage invalid, one must prove one of the following grounds:1. A spouse lacked the capacity to consent to the marriage. For instance, a spouse was suffering from a mental problem or was under the influence of drugs or alcohol at the time the marriage was made official.2. A spouse only agreed to the marriage because of force, duress, or fraud. Importantly, for fraud to be a viable ground to invalidate the marriage, the fraud must go to the essentials of the marriage (or, said another way, it must go to the heart of the marriage). By way of example, if a spouse only married to avoid deportation and never intended on living with the other party, one could argue fraud on the marriage.3. One of the spouses lacked the physical capacity to consummate the marriage.4. One of the spouses was under the age of 18 at the time the marriage was made official and did not obtain the approval of a parent, guardian or Illinois judge.5. The marriage is prohibited by law. This is applicable where, for instance, one spouse is still legally married, or the marriage is incestuous (i.e., the spouses are closely related by blood).In the event children are born to a marriage which is later invalidated, Illinois law provides that children born or adopted during such a marriage are the lawful children of the parties. Thus, there are no legitimacy issues for such children and they have the same legal rights as the children of valid marriages. However, the financial ramifications of a marriage that is declared invalid can be very serious, as the parties are not entitled to the same benefits as parties to a valid marriage, which includes the right to divide property and the right to receive maintenance (formerly known as alimony). One exception to this rule is if a person married someone in good faith who was already married, the court can grant that spouse the same rights as a legal spouse.In deciding whether to pursue a divorce or declaration that your marriage is invalid, it is important to consult with an attorney who specializes in matrimonial law in order to help you assess your chances of success and the legal ramifications of each option, keeping in mind that it is rare for a court to declare a marriage invalid.