This study was designed to test the hypothesis that mindfulness involves sustained attention, attention switching, inhibition of elaborative processing and non-directed attention. Healthy adults were tested before and after random assignment to an 8-week Mindfulness-Based Stress Reduction (MBSR) course (n = 39) or a wait-list control (n = 33). Testing included measures of sustained attention, attention switching, Stroop interference (as a measure of inhibition of elaborative processing), detection of objects in consistent or inconsistent scenes (as a measure of non-directed attention), as well as self-report measures of emotional well-being and mindfulness. Participation in the MBSR course was associated with significantly greater improvements in emotional well-being and mindfulness, but no improvements in attentional control relative to the control group. However, improvements in mindfulness after MBSR were correlated with improvements in object detection. We discuss the implications of these results as they relate to the role of attention in mindfulness. Copyright © 2007 John Wiley & Sons, Ltd.