Web-based psychological interventions aim to make psychological treatments more accessible and minimize clinician input, but their effectiveness requires further examination. The purposes of the present study are to evaluate the outcomes of web-based interventions for treating depressed adults using meta-analytic techniques, and to examine moderating effects on these interventions. A random-effects analysis yielded a medium effect of web-based interventions compared to controls, with a significant reduction in depression and improvement in well-being. Regression analysis revealed moderating effects of human support and inclusion of reminders in treatments for depression. Also, mean attrition rates were similar to face-to-face treatment, moderated by inclusion of human support. Future research on client suitability and clinical significance are needed. Trials on web-based interventions are encouraged to address quality constraints apparent in existing studies, namely the need for explicit acknowledgment of multiple publications, ensuring quality of control groups, and careful reporting of methods and results. It was concluded that web-based interventions are effective ways of treating depression and enhancing well-being, particularly if supplemented with personal engagement.