Mindfulness has been defined as a quality of “enhanced attention to and awareness of current experience or present reality” (p. 822, Brown & Ryan, 2003). Studies of mindfulness-based interventions have shown beneficial effects on well-being–both physical and psychological. However, few studies have addressed the mechanisms underlying these effects—using an experimental approach with conditions that control for nonspecific effects of mindfulness training (e.g., expectancy, relaxation). We examined the effect of mindfulness meditation (MM) on attentional control in emotional contexts. In Study 1, MM practitioners with varying durations of MM experience categorized tones presented 1 or 4s following the onset of affective pictures. Reaction times (RTs) to tones for affective minus neutral pictures provided an index of emotional interference. Study 2 was a controlled, experimental study in which participants received MM training, relaxation meditation (RM) training, or no intervention (waiting-list control; WLC). Behavioral, self-report, and psychophysiological measures were administered before and after a 7-week intervention period. In Study 1, participants with more MM experience showed less interference from affective pictures and reported higher mindfulness and psychological well-being. While both MM and RM resulted in smaller skin conductance responses to unpleasant pictures and increased well-being, reductions in emotional interference from unpleasant pictures were specific to MM. These findings indicate that MM attenuates prolonged reactivity to emotional stimuli, and this may in turn account for improvements in well-being.