mHealth (mobile health) serves as a potential solution for circumventing barriers to traditional psychotherapy, but few studies evaluate mHealth technologies available in real-world settings with real-world users. This study evaluated the extent to which MoodTools, a self-help app for depression, circumvents barriers to traditional psychotherapy and engages users. App behavior from 159,00 Android users were assessed. Results showed that MoodTools could circumvent barriers to traditional psychotherapy, as it was downloaded in 198 countries, and the number of users was positively correlated with rates of unmet mental health need in the US. App use during and outside of traditional business hours were not significantly different. Regarding engagement, app sessions averaged 4 minutes and half of users returned to the app after their first session. There was no correlation between users’ initial depressive symptom severity score and total amount of time spent in MoodTools. Implications and future directions are discussed.