Mindfulness meditation provides promise for stress relief and well-being. However, most non-clinical studies suffer major limitations. We addressed many of the limitations through larger samples, a design combining a randomized active-controlled trial (RCT) with cross-sectional analysis of long-term training, and complementary brain and behavioral measures. Mindfulness meditation involves paying attention to the present moment, with a non-reactive stance toward experience. This dissertation rigorously tested the impact of mindfulness meditation training on the neural correlates of emotional nonreactivity, resting state functional connectivity (RSFC) in brain networks associated with attention and mind-wandering, and structural neuroplasticity. We examined the impact of short-term training with Mindfulness-Based Stress Reduction (MBSR), which is widely used, extensively tested and has demonstrated clinical efficacy. In Chapter 1, we examined amygdala reactivity and functional connectivity with ventromedial prefrontal cortex (VMPFC) during emotional stimuli, which have been implicated in emotion regulation. Mindfulness meditation was associated with reduced amygdala reactivity and increased functional connectivity with VMPFC. Increased amygdala-VMPFC functional connectivity was associated with decreased amygdala reactivity from pre- to post-intervention. In Chapter 2, we replicated and extended prior work showing increased RSFC between posterior cingulate cortex (PCC) and lateral prefrontal cortex (LPFC), which are implicated in mind-wandering and attention, respectively. Increased PCC–LPFC RSFC is hypothesized to reflect better attentional control of mind-wandering. In support of this hypothesis, we found that increased self-reported attention was associated with stronger PCC–LPFC RSFC from pre- to post-intervention. In Chapter 3, we attempted to replicate and extend research showing changes in regional gray matter volume (GMV) associated with mindfulness meditation training. However, there were no significant differences in GMV between meditators and controls. Yet, time practicing mindfulness meditation was associated with differences in amygdala and hippocampus GMV. This dissertation provides evidence for tangible neural changes associated with mindfulness meditation training, which are consistent with hypothesized benefits in emotional nonreactivity and attention. The lack of replication of group differences in brain structure highlights the need for publishing null results, and for rigorous RCTs of MBSR in community samples. Finally, effects of practice time were evident across measures, underscoring the importance of sustained meditation practice.