Background: Research support for a variety of health benefits of mindfulness-based interventions for adults is robust. These include management of stress, anxiety, and depression; as a supportive treatment for eating disorders, PTSD, and psychosis; improved sleep; chronic pain management; support for tobacco, alcohol, and substance abstinence; and as adjunctive treatments for serious or chronic medical illnesses such as HIV, cancer, and heart conditions. As is typical with newer interventions, mindfulness intervention research that evaluates similar benefits for youth began later and is less advanced. This paper presents an in-depth, critical analysis of the state of the research on mental and physical health benefits of mindfulness-based interventions for children and adolescents. Method: Electronic databases and other resources were searched for the period from January 2000 to July 2018 to locate empirical studies of mindfulness-based interventions for children or adolescents that primarily assessed physical or mental health outcomes. Results: Data from 25 published studies and 5 meta-analyses or systematic reviews are presented, along with a critical evaluation of the strengths and limitations of these studies. Conclusion: Mindfulness research for youth has progressed considerably over the past decade. Nevertheless, the methodological limitations of many studies are significant. This, along with the heterogeneous nature of the studies, makes it difficult to arrive at any firm conclusions. However, the generally positive findings across many studies appear promising. Considered as a whole, current evidence suggests that mindfulness may be effective in improving the health and well-being of children and adolescents. Well-designed and carefully implemented studies will continue to advance our knowledge of mindfulness-based interventions for youth.