The empirical literature provides increasing support for the efficacy of mindfulness training in the treatment of numerous problems and disorders. However, fewer studies have examined the mechanisms through which these beneficial outcomes are obtained. This article summarizes recent research examining three primary questions related to the mechanisms underlying mindfulness-based treatments: do people who practice mindfulness learn to be more mindful of the experiences of daily life? Is an increased general tendency to be mindful related to reduced symptoms and increased well-being? If so, then what psychological processes account for the beneficial effects of increased mindfulness? Recent studies suggest that the practice of mindfulness develops the ability to observe and describe present-moment experiences nonjudgmentally and nonreactively and to participate with awareness in ongoing activity. Increased mindfulness, in turn, appears to mediate improvement in psychological functioning, probably by cultivating an adaptive form of self-focused attention that reduces rumination and emotional avoidance and improves behavioral self-regulation.