The psychotherapeutic process is a path of change guided by a psychotherapist, who helps to modify dysfunc-tional thoughts, emotions and behaviours to reduce psychological suffering, resolve negative mental patterns, improve psychological well-being and promote a more functional adaptation to life. This process is so complex that its evolution is unpredictable: even minimal variations in the initial conditions produce effects which can be very significant and are not deterministically connected to the conditions themselves. For this reason, it is essential to verify the effectiveness of the treatment through an evidence-based approach: return and/or reduc-tion of symptoms compared to the baseline and maintenance of the same, transformation of the variables typ-ical of a particular disorder (depression, OCD, etc.) and of the peculiarities of that particular subject, and the progress of the relationship that this transformation produces and sustains over time.

Therefore, to have an accurate representation of the process of change, it is necessary to have an assessment tool that can detect useful indicators significant for improving the therapist-patient relationship and treatment outcome throughout the duration of therapy.

One tool that seems to meet these characteristics, although still statistically insignificant, is the Psychotherapy Evaluation Questionnaire (PEQ) designed and developed by one of the authors (G.M.G.), which allows the ef-fectiveness of therapy to be investigated by examining the following areas: 1) Therapeutic relationship, 2) Mo-tivation for therapy, 3) Adherence to therapy, and 4) Outcomes.