Recent research has demonstrated that higher levels of mindfulness are associated with greater psychological and physical health. However, the majority of this research has been conducted with adults; research is only beginning to examine the effects of mindfulness among adolescents. Further, research into adolescent mindfulness has typically conceptualized mindfulness as a unidimensional phenomenon and has not yet examined multidimensional models of mindfulness that have emerged in the adult literature. Further, the mechanisms through which mindfulness influences these outcomes are presently unclear. The present study examined the effects of three facets of mindfulness among adolescents. Seventy-eight adolescents (61% female, 94% Caucasian, M age = 16) completed a measure of dispositional mindfulness at baseline. Participants then completed measures of daily stress, dysphoric affect, and state rumination over a 7-day period. Multilevel modeling analyses revealed that facets of mindfulness (i.e., nonreactivity and nonjudgment) were associated with lower levels of dysphoric mood. Mindfulness interacted with daily stress to predict later dysphoria; less mindful individuals were particularly vulnerable to the negative effects of stress. Finally, analyses demonstrated that the effect of the Mindfulness × Stress Moderation was significantly mediated by increases in daily rumination. These findings support the importance of mindfulness among adolescents and help to elucidate the mechanisms through which mindfulness influences psychological health.