We hypothesize that there is a decrease in Repetitive Negative Thinking (RNT) in the group performing the more intensive version of the Cognitive Control Training (CCT), with such a decrease being significantly smaller in the group performing the active control version. These changes in RNT may mediate effects of training on depression-/anxiety-/stress-related symptoms (measured concurrently and/or at follow-up). As such, our primary instruments are the PTQ (Ehring et al., 2011) and DASS (Lovibond & Lovibond, 1995) for quantifying RNT and the various symptom clusters, respectively. In addition, the CEQ (Devilly & Borkovec, 2000) will be included to check for differences between conditions with regards to credibility and expectancy of the intervention (both before and after the training period). Given that the mechanisms of Cognitive Control have been implicated in the tendency to ruminate, we predict that adding CCT on top of existing group-based programs results in a more pronounced reduction in RNT (as compared to the active control condition). RNT is in turn expected to predict symptoms (as measured by the DASS). Provided that this study is among the first to investigate the combined effects of CCT and group therapy, there are obviously still many degrees of freedom. As there is still little known about the topic (e.g., the question of ceiling effects related to the group therapy, whether or not adding CCT indeed changes the magnitude of the total effect, the timing of the effects when doing both interventions in parallel,…), this project also has a more explorative aim. The CERQ (Garnefski, Kraaij, & Spinhoven, 2001) and ATQ (Derryberry & Rothbart, 1988) are included as secondary outcome measures. The former allows for a more broad investigation of effects of the intervention on emotion regulation (as it measures other strategies than RNT, including strategies that are considered to be more adaptive). The latter is interesting because of the Effortful Control factor (EC-ATQ, consisting of ‘Inhibitory Control’, ‘Activation Control’ and ‘Attentional Control’), which is conceptually related to Cognitive Control/Executive Functioning. In practice however, the corresponding measures are likely tapping into different aspects of the same concept, with the Paced Auditory Serial Addition Task (‘PASAT’: Gronwall, 1977) capturing the behavioral dimension and the EC-ATQ capturing subjective experience. In short, this project aims to detect an effect of CCT on RNT when combining it with a group-based emotion regulation intervention. *Derryberry, D., & Rothbart, M. K. (1988). Arousal, affect, and attention as components of temperament. Journal of Personality and Social Psychology,55(6), 958–966. https://doi.org/10.1037/0022-3514.55.6.958* *Devilly, G. J., & Borkovec, T. D. (2000). Psychometric properties of the credibility/expectancy questionnaire. Journal of Behavior Therapy and Experimental Psychiatry, 31(2), 73–86. https://doi.org/10.1016/S0005-7916(00)00012-4* *Ehring, T., Zetsche, U., Weidacker, K., Wahl, K., Schönfeld, S., & Ehlers, A. (2011). The Perseverative Thinking Questionnaire (PTQ): Validation of a content-independent measure of repetitive negative thinking. Journal of Behavior Therapy and Experimental Psychiatry, 42(2), 225–232. doi:10.1016/j.jbtep.2010.12.003* *Garnefski, N., Kraaij, V., & Spinhoven, P. (2001). Negative life events, cognitive emotion regulation and emotional problems. Personality and Individual Differences, 30, 1311– 1327. https://doi.org/10.1016/S0191-8869(00)00113-6* *Gronwall, D. M. A. (1977). PACED AUDITORY SERIAL-ADDITION TASK: A MEASURE OF RECOVERY FROM CONCUSSION. Perceptual and Motor Skills, 44(2), 367–373. https://doi.org/10.2466/pms.1977.44.2.367* *Lovibond, P. F., & Lovibond, S. H. (1995). The structure of negative emotional states: Comparison of the Depression Anxiety Stress Scales (DASS) with the Beck Depression and Anxiety Inventories. Behaviour Research and Therapy, 33(3), 335–343. https://doi.org/10.1016/0005-7967(94)00075-U*