It is regularly observed that in France “psychiatric expertise” and “psychological expertise” for criminal trials can present two pitfalls in their implementation: the lack of experts (psychiatrists experts in particular) and possible content that is sometimes erroneous. Given the number of psychiatrists and psychologists, these two terms of expertise could be abandoned in favor of a single concept of “mental expertise” carried out indifferently by psychiatrists or by psychologists selected as being well trained, professionally experienced and competent to carry out these missions. This decompartmentalization with the establishment of some other major principles (creation of a clinical and legal consensus of mental expertise, obligation of harmonized and updated training of experts, taking into account the professional experience of experts, time spent and appropriate periods for carrying out expert assessments, revaluation of expert acts, development of research on expertise, creation of body(ies) for the control and regulation of expert practices) could make it possible to make available to justice and litigants with sufficient numbers of quality experts throughout the national territory.