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Ample evidence exists for the assumption that childhood trauma is associated with the onset and recurrence of depressive disorders (Chapman et al., 2004; Ferguson & Dacey, 1997; Nanni et al., 2012). However, the causal mechanisms between childhood trauma and the subsequent develop-ment of depression have not been sufficiently studied. To date, no studies have investigated gen-eral emotion regulation as the mediating mechanism between childhood trauma and depression severity as well as depression persistency in a clinical sample. Moreover, research on this topic has been focused thus far on only general emotion regulation or single dysfunctional emotion regula-tion strategies (i.e., rumination), not taking a variety of different emotion regulation skills into account. Since the relapse rate for Major Depressive Disorder (MDD) is very high (Vittengl et al., 2007; Westen & Morrison, 2001), there is a pressing need to identify potential factors that prevent re-currence of depressive symptoms and that help maintain treatment success once it is achieved. Prospective studies have indicated that emotion regulation is capable of predicting depressive symptoms (Berking et al., 2014; Radkovsky et al., 2014; Wang et al., 2014). However, it is not known whether emotion regulation remains a predictor for subsequent depressive symptoms fol-lowing psychotherapy for depression. Furthermore, there are yet no studies analyzing whether emotion regulation predicts time to MDD relapse in depression remitters after psychotherapy. There is yet no research on the potentially different relevance of a variety of specific emotion regu-lation skills in predicting depressive symptoms and time to MDD relapse following treatment. This dissertation aims to identify general adaptive emotion regulation as a crucial factor for devel-opment and maintenance of depression. Another emphasis was put on the relevance of specific emotion regulation skills. In a longitudinal study, we tested the hypothesis of adaptive emotion regulation as a predictor of depressive symptoms up to one year after inpatient depression treatment (Study 1). Among treat-ment responders only, higher general emotion regulation predicted lower depressive symptoms three months, but not twelve months after treatment. The specific emotion regulation skill will-ingness to confront predicted lower depressive symptoms twelve months after treatment and the emotion regulation skill acceptance predicted lower depressive symptoms three and twelve months after treatment. In a cross-sectional study, we tested the hypothesis of emotion regulation as a mediator of the effect of childhood trauma on depression severity and depression lifetime persistency in inpatient treated persons with MDD (Study 2). General emotion regulation and the emotion regulation skills willingness to confront were partial mediators of the association between childhood trauma and later depression severity as well as depression lifetime persistency. In a longitudinal study, we investigated prospective effects of adaptive emotion regulation and the time to relapse into depression after successful inpatient treatment (Study 3). More effective gen-eral emotion regulation as well as the specific emotion regulation skills emotional acceptance and tolerance, compassionate self-support, willingness to confront challenging situations as well as the ability to modify negative affects predicted longer time to MDD relapse. Future studies such as randomized controlled studies on formerly depressed and maltreated per-sons will have to examine whether increasing adaptive emotion regulation with specific interven-tions can help to reduce the subsequent depression risk. Furthermore, future studies on formerly depressed will have to show whether increasing adaptive emotion regulation can contribute to a protection against a relapse into Depression.