Mindfulness-based interventions (MBIs), which train people to monitor present-moment experiences from an accepting perspective, improve a variety of attention, emotion, social, stress, and health outcomes. Through the lens of monitor and acceptance theory (MAT), this chapter explores mechanisms of MBIs on these personal and social well-being outcomes. We review dismantling experiments that test MAT predictions by isolating monitoring and acceptance skills trained in MBIs. Consistent with MAT, evidence suggests that monitoring alone is sufficient for improving attention in daily life, and that monitoring and acceptance combined improve daily life stress, physiological stress reactivity, pain intensity, negative affect, social functioning, and positive affect. Although short-term monitoring by itself can intensify symptoms, evidence from longer MBIs suggests a revision to MAT—namely, that systematic monitoring training does not exacerbate (or mitigate) affective reactivity. We conclude with directions for future research, including questions about dosage, individual differences, the possibility of isolating acceptance skills, and measurement. Ultimately, a mechanistic understanding of MBIs can help to tailor interventions for specific needs.