Witnesses are very important. The persons submitted as witnesses are normally nominated by the parties to the marriage. They must be willing to be interviewed confidentially by the Tribunal about what they know of the marriage. They are not simply character referees; they must have some knowledge of the marriage under scrutiny.

It may also be necessary to ask the applicant's written permission to obtain relevant medical reports or to request professional evaluation by a psychologist. Due to the very personal nature of the information gathered in nullity cases, every effort is made to preserve confidentiality in the process.