SUMMARY This PhD thesis comprises four studies focused on different aspects of thought control. In study 1 (n = 540) the latent factor structure of the White Bear Suppression Inventory (WBSI; Wegner & Zanakos, 1994) and the Thought Control Questionnaire (TCQ; Wells & Davies, 1994) was examined using confirmatory factor analyses. The tested models fit the data poorly, although the results suggested a two-factor and a five-factor structure for the WBSI and the TCQ, respectively. The two factors from the WBSI (presence of intrusive thoughts and chronic thought suppression) showed a significant relationship with depressive symptoms, obsessive-compulsive complaints and pathological worry, whereas only two of the TCQ factors (punishment and worry) were associated with these psychopathological symptoms. In study 2 (n = 211) a new self-report instrument was developed and validated, in order to assess individual differences in thought control ability (Thought Control Ability Questionnaire, TCAQ). Data analysis yielded a one-dimensional instrument with 25 items that showed high internal consistency and test-retest reliability. The TCAQ had significant negative relationships with some measures of emotional vulnerability and psychopathology. The main goal of study 3 (n = 76) was to examine whether individuals can successfully suppress an intrusive thought confronting a reminder of it, an effective suppression technique employed on memory research (Anderson & Green, 2001). The examination of the annoyance associated with the intrusions indicated that those individuals instructed to suppress the intrusions without confronting the reminder maintained at long-term the same level of discomfort reported at baseline, whereas the participants from the other two conditions reduced the discomfort level. This result suggests that the confrontation with a reminder is a recommendable strategy for emotion regulation. Finally, in study 4 (n = 120) we extended the previous findings, comparing the efficacy of different thought suppression strategies: suppression-only, suppression with focused distraction, and suppression confronting a reminder of the target thought. Data analysis showed that those subjects instructed to employ focused distraction reported a low number of intrusions in comparison with the control condition, demonstrating that distraction is an adaptive thought control strategy.