There is a misconception that an annulment is simply a Catholic divorce; nothing could be further from the truth. Divorce is a civil law procedure in which one or both persons decide to end an existing marital contract.
An annulment is different. The Catholic Church teaches that once a sacramental marriage is constituted by the valid, mutual consent of the couple, only death can break the marriage covenant. Marriage is forever. An annulment is an official judgment on the part of the Church that (1) there was an impediment that prohibited a valid marriage, or (2) a defect of the consent of one or both parties rendered the marriage consent invalid.
The various types of annulments will be described further on.