BACKGROUND: Depression among adolescents is rising globally and is the leading cause of illness and disability among adolescents. While antidepressants and psychotherapy are effective, only about 40% of depressed adolescents receive treatments due to lack of professionals and barriers such as cost and personal obstacles including stigma, lack of motivation, and negative perceptions of treatment. Use of alternative and complementary treatments for depression is growing. One such treatment is mindfulness meditation. OBJECTIVE: We examined the effects of mindfulness interventions on depression among adolescents and explored the moderator effects of participants, methods, and intervention characteristics. METHODS: We searched 17 databases from their inception to April 2019 to identify studies written in English. Search terms included depress* AND mindful* OR meditat* AND adolescen* OR student*; 29 studies met inclusion criteria. Two researchers independently coded data from all primary studies. Discrepancies were discussed with a third researcher to reach consensus. Using the random effects model, we computed the effect sizes (ESs) of mindfulness interventions on depression using standardized mean differences (Hedge's g) with 95% confidence intervals (CI). Funnel plot, Q statistics, and I RESULTS: Across 29 studies (N=3688), 1839 adolescents participated in mindfulness interventions; 1849 served as controls. Mean ages ranged from 10.2 to 19.5 years. Mindfulness groups showed reduced depression compared to control groups (g=.14, 95%CI[.01-.28], p<.042). Funded studies showed greater improvement in depression (g=.34, 95%CI[.09-.58], p<.008) compared to unfunded (g=.05, 95%CI[-.12-.22], p<.554). Interestingly, while only two research teams studied mindfulness-based cognitive therapy, they showed trends toward improvement (p=0.09) in depression (g=.76, 95%CI[.18-1.34], p<.010, s=2) compared to adapted mindfulness interventions (g=.13, 95%CI[-.04-.30], p<.140, s=16) or mindfulness-based stress reduction (g=.07, 95%CI[-.16-.29], p<.559, s=11). Mindfulness interventions with individual counseling tended (p=0.09) to improve depression (g=.46, 95%CI[.07-.85], p<.021, s=3) more than without (g=.10, 95%CI[-.04-.24], p<.168, s=26). Depression improved more when follow-up measures occurred further from the intervention (Slope=.002, τ CONCLUSION: Mindfulness interventions are mildly effective interventions to reduce depressive symptoms among adolescents. Clinicians trained in mindfulness interventions might encourage mindfulness meditation as adjunctive/alternative treatment for adolescents with mild or moderate depressive symptoms as well as for at-risk adolescents to prevent depression. Funding, type of mindfulness interventions, individual counseling, and time to follow up were moderators of the effects of mindfulness interventions on depression in adolescents.