Abstract: Formal feedback involves the routine collection of client feedback to track their progress, identify not-on track clients, and facilitate adjustment of therapy to prevent treatment failure. The need for formal feedback is based on previous findings that many clients quit therapy prematurely or have negative outcomes. Unfortunately, therapists usually do poorly in predicting treatment failures. However, formal feedback shows a superior ability to identify clients who are not on track in the early stage of psychotherapy, which makes corrective intervention possible in the coming sessions. Historically, the development of formal feedback occurred in two stages. In the first stage (about 1996-2011), researchers developed client feedback systems and examined the effectiveness of formal feedback. But so far, there are only two client feedback systems supported by randomized clinical trials. The first is the Outcome Questionnaire System, and the other is the Partners for Change Outcome Management System. In the second stage(since about 2011), clinical researchers focused on clinical utility, including developing brief questionnaires to track clients’ progress and integrating feedback data into clinical process. Formal feedback is now widely used in various clinical settings, including individual, couples and group therapy. Two recent meta-analyses showed that, in the feedback condition, there was a 50% reduction in the proportion of clients who got worse at the end of therapy, and the rate of significant improvement was several times higher than in the treatment as usual condition. This research introduced the application of formal feedback in different therapy setting, and recommended some alternative client feedback systems that have been proved to be effective to enhance treatment outcome in individual, couples and group therapy. In addition, researchers discussed the influence of clients’ level of initial distress on feedback effect. The formal feedback provided to therapists is also helpful as part of clinical supervision. Firstly, formal feedback can help to evaluate the effect of clinical supervision from the perspective of clients, which may be more objective and accurate. Secondly, novice therapists may use formal feedback from clients to identify what they need help with during supervision, and to help them learn from their failures to become more effective. Thirdly, formal feedback can provide indirect information about the effectiveness and direction of clinical supervision. Supervisors can teach targeted techniques and skills to supervisees according to patterns of formal feedback across clients. In future research, it will be important to explore therapists' attitudes toward formal feedback, and identify the possible barriers and facilitators of this approach from the perspective of individuals, organizations and practical concerns. This information will then lay the groundwork for promoting positive attitudes towards formal feedback. In addition, it will be of significance to extend the application value of formal feedback, such as using feedback to promote the development of therapists’ professional skills, and integrating information gained from formal feedback into novice therapists’ training. Finally, more localized studies of formal feedback should be conducted, including developing client feedback systems and establishing the norms of client feedback data based on cultural context.