Study must be registered under the sponsor instead of the site, so we have created a new posting in the sponsor's account.

The investigators are testing the efficacy of Smartphone-delivered cognitive behavioral therapy (CBT) treatment for major depressive disorder (MDD). The investigators hypothesize that participants receiving app-CBT will have greater improvement in QIDS-C scores than those in the waitlist condition at treatment endpoint (week 8).

The primary aims of this study are to test the efficacy of a Smartphone-based CBT treatment for adults with MDD recruited nationally. Eligible subjects (N=112) will be randomly assigned to 8 weeks of Smartphone-delivered CBT for MDD either immediately, or after a 8-week long waiting period (50-50 chance). The investigators hypothesize that Smartphone-delivered CBT for MDD will be feasible and acceptable to individuals with MDD, and that it will lead to greater reductions in MDD symptom severity compared to the passage of time (waitlist control).

Inclusion Criteria:

• At least 18 years of age
• Current diagnosis of primary DSM-5 MDD, based on MINI
• Currently living in the United States

Exclusion Criteria:

• Psychotropic medication changes within 2 months prior to enrollment (Participants taking psychotropic medication must have been on a stable dose for at least 2 months prior to enrollment and not change medication during study period)
• Past participation in ≥ 4 sessions of CBT for depression
• Current severe substance use disorder
• Lifetime bipolar disorder or psychosis
• Acute, active suicidal ideation as indicated by clinical judgment and/or a score ≥ 2 on the suicidal ideation subscale of the C-SSRS
• Concurrent psychological treatment
• Does not own a supported mobile Smartphone with a data plan
• Lack of technology literacy that would interfere with ability to engage with smartphone treatment