Effective treatment of suicidal patients is a priority in suicide prevention efforts. Understanding the mechanisms underlying treatment is crucial for identifying individuals who are likely to benefit from suicide-specific treatment and for determining optimal treatment settings. The Attempted Suicide Short Intervention Program (ASSIP) has been shown to reduce the risk of repeat suicide attempts by approximately 80% over 24 months (Wald ?21 = 13.1, 95% CI 12.4-13.7, p < 0.001). ASSIP consists of three to four sessions that focus on developing a shared understanding of the patient's suicidal behavior in a biographical context, identifying vulnerabilities and triggers, and creating a personalized crisis plan. Central to ASSIP is the establishment of a trusting therapeutic relationship, which is maintained through two years of follow-up letters. This presentation will highlight different mechanisms of action of this psychological intervention, emphasizing its clinical process elements. For example, there are individual differences in the longitudinal development of reasons for living (RFL) and reasons for dying (RFD) between the intervention and control group. In contrast to RFL, RFD decreased significantly over the 24-month period, with a greater decrease in the ASSIP group (t1: 2.32 to t5: 0.51) than in the control group (t1: 1.90 to t5: 1.04) (b=-0.02; p=.004). However, working through dysfunctional coping strategies (ASSIP: 11% less dysfunctional coping; W = 1316, p = 0.011, r = 0.21) seems to be an important complement to the development of problem-oriented coping strategies (ASSIP: 6% more problem-oriented coping; W = 2217, p = 0.029, r = 0.17) in order to be able to cope with suicidal crises. Furthermore, new research approaches such as the recording of movement synchrony between patient and therapist using Motion Energy Analysis (MEA), and its relevance for understanding the therapeutic process, are outlined. Nonverbal behavior in therapy, was found to play an important role in building a good therapeutic alliance and was associated with positive therapeutic outcome. In addition, the use of Ecological Momentary Assessment (EMA) in the longitudinal NePsyASSIP project is presented and its relevance for understanding the therapeutic process is discussed.