Objectives: Mindfulness-based stress reduction (MBSR) has been found to reduce psychological distress and improve psychological adjustment in medical, psychiatric, and nonclinical samples. We examined its effects on several processes, attitudes, and behavior patterns related to emotion regulation. Design: Fifty-six adults were randomly assigned to MBSR or to a waiting list (WL). Results: Compared with WL completers (n = 21), MBSR completers (n = 20) reported significantly greater increases in trait mindfulness and decreases in absent-mindedness, greater increases in self-compassion, and decreases in fear of emotions, suppression of anger, aggressive anger expression, worry, and difficulties regulating emotions. The WL group subsequently received MBSR, and the two groups combined showed significant changes on all of these variables from pre-MBSR to post-MBSR, and on all except the 2 anger variables from pre-test to 2-month follow-up, as well as significant reductions in rumination. Conclusion: An 8-week mindfulness training program might increase mindful awareness in daily life and have beneficial impact on clinically relevant emotion regulation processes. © 2011 Wiley Periodicals, Inc. J Clin Psychol 68:1–15, 2011.