In cases of nullity of marriage the following are competent: 1° the Tribunal of the place where the marriage was celebrated; 2° the Court of the place where one or both parties have their domicile or quasi-domicile; 3° the Tribunal of the place where in fact most of the evidence is to be gathered (can. 1672).

The process begins with the deposit of the «libellus», an act in which the facts and legal reasons for which the declaration of nullity is requested are summarily described. Once the libellus has been admitted and the "doubt" agreed (the formula with which the ground of nullity that will be investigated during the process is established), the preliminary investigation begins with the summons and examination of the parties. The witnesses are then examined and – in the cases expressly provided for (impotence and mental incapacity) – an expert report is arranged. Once the preliminary investigation was completed, after the filing of the defense brief of the lawyer – the so-called Restrictus – and the observations of the Defender of the Bond – the cc.dd. Animadversiones – the case is sent to a decision.

The sentence is pronounced by a Panel normally made up of three judges who will establish whether or not the nullity of the marriage has been proved in the case for the abducted head/s.

In the event of an appeal against an affirmative sentence, the Court of Second Instance will first of all assess whether the appeal is founded or is only made for delaying purposes. In the latter case, he will confirm the sentence that decided the nullity of the marriage. In the event that the appeal is deemed justified, a new phase of evidence collection will open at the end of which a new sentence will be pronounced. If this has declared the marriage null, the process will end; otherwise, in the face of two different sentences, the third degree of judgment will be decisive.

The appeal can be brought before the competent ecclesiastical court or directly to the Roman Rota.

Following the sentence declaring nullity, marriage is tamquam non esset, that is, as if it had never existed: this allows for the celebration of a new marriage and regular access to the sacraments (where the personal situation of the party has not permitted them for ago).