Depression, anxiety, and stress affect the lives of millions of individuals worldwide. Mindfulness-based therapy methods are a relatively new way of treating individuals with these symptoms. In this study, we conducted a meta-analysis to study the effectiveness of mindfulness-based therapy on depression, anxiety and stress. We utilized PsycInfo to locate 15 articles that measured the effectiveness of mindfulness-based methods. The effect size for each study was calculated, and then, the overall average weighted effect size was calculated. We hypothesized that mindfulness-based therapy methods would have a moderate to large effect on depression and stress but a small to moderate effect on anxiety.