When one applies to a church Tribunal for a decree of nullity of marriage one is alleging that, at the time of marriage, the consent of one or both of the parties was seriously flawed and thereby a marriage did not come into being.
A declaration of marriage nullity is a judgement reached by the Tribunal that a given marriage was invalidly contracted at the moment of consent. The judgment is given only after a “judicial process”, that is, as the result of an investigation carried out by an ecclesiastical judge.
The investigation is carried out in accordance with the Church’s own legal procedures as contained in the 1983 Code of Canon Law. This Code includes laws about preparing for marriage, getting married, living married life and deciding whether or not a marriage brought before a Tribunal is null.