Annulment, in law, a judgment of a court that a marriage was void from its beginning. There are two types. In one type, the marriage is automatically void upon discovery of some fact—bigamy, for example. In the second type, a court must decide whether facts presented by one spouse make the marriage void. Fraud is often the cause of an annulment suit. For example, a couple may have agreed to have a family and one spouse may later refuse to consider this. In such instance, annulment is generally granted. If one spouse has claimed to be rich and is not, however, such fraud is not grounds for annulment.

The Roman Catholic Church, which does not recognize divorce, does grant annulments on various religious grounds, few of which are the same as legal grounds.