An expertise is a report created and presented by a professional, a judicial expert, generally to answer questions posed by a judge with the aim of helping the latter to have sufficient knowledge to issue a sentence. This is dictated in article 335.1 of Law 1/2000 of Civil Procedure.[1]​.

The expert opinion can also be useful for those people who want to submit a report as judicial evidence. Since this person does not have all the technical knowledge to do it, he or she can obtain the help of a judicial expert to create a report with a reasoned and understandable presentation and conclusion for all those who are not experts in the matter. The report must be the main part of the claim. It serves to validate parental capacity, rule out pathologies, make observations, study the family environment and many other aspects, as well as to present all the tests that are available and performed (diagnostic tests, emails, photos, recordings, medical reports...). All of this, well presented and argued, forms the fundamental basis to have the option or increase the possibilities in a family court, a criminal trial or other procedures.

An expert opinion must comply with the specific laws of each country; however, in general, expert opinions can be carried out through official (that is, state) or private judicial experts.

The current separation and divorce processes, which are increasingly frequent, require a report attached to the separation/divorce application, to analyze, study and propose measures on issues such as:

Reports must be structured following a logical and necessary order in order to draw valid, reliable, conducive and relevant conclusions regarding the object of the report. Thus, some of the sections whose development is necessary are:

As can be deduced from the above, the judicial expert opinion contains a large number of diverse elements and of such complexity that they require a thorough evaluation, detailed and careful by the examiner since it compromises the lives of individuals at all levels and areas of adjustment, for which any error or omission in any detail can be truly harmful to the process and to the information that is provided to the legal entity that requests the test, without also taking into account the legal, ethical and professional commitment that is involved in the task. of the professional. Likewise, being a means of proof as part of a legal process requires knowledge of legal aspects that allow the work to be carried out in a more optimal way and in accordance with the needs and demands of each situation.

The expertise follows a procedure, in which it goes through different phases,[3]​ which are as follows: