Background: People using apps for mental health and wellbeing are likely to try multiple apps over time. In general, people use apps to meet immediate needs, and often use a variety of apps to meet larger goals (for example people may have multiple apps to manage various transportation needs). IntelliCare is a mental health app platform that was designed with these principles in mind: the apps are elemental in that each app targets a different change strategy; they are simple and brief to use; and they are eclectic, allowing the user to select which strategies are useful to them. While this may improve engagement, it creates the same challenges faced by users of app stores. Thus, mental health app platforms will require navigation aids, such as recommender systems that can quickly get a person to an app that is useful. Objective: As a first step towards developing navigation and recommender tools, this study explored app use patterns across the IntelliCare platform, and their relationship to depression and anxiety outcomes. Method: This secondary analysis of the IntelliCare Field Trial recruited people with depression and/or anxiety. Participants received 8 weeks of coaching, primarily by text, and weekly recommendations for apps. App use metrics included frequency of use and lifetime use were defined. Depression and anxiety, measured using the PHQ-9 and GAD-7, were assessed at baseline and end of treatment. Ordinal logistic regression models, log-rank tests and cluster analysis were utilized to determine patterns of use, and if these use metrics alone, or in combination, predicted improvement or remission(I/R) in depression or anxiety. Results: The analysis included 96 people with depression and/or anxiety. Peole generally followed recommendations to download and try new apps each week. Apps clustered into 5 groups: Thinking (apps that targeted or relied on thinking), Calming (relaxation and insomnia), Checklists (apps that used checklists), Activity (behavioral activation and activity), and Other. Both overall frequency of use and lifetime use were predictive in response for depression and anxiety. The Thinking, Calming, and Checklist clusters were associated with improvement in depression and anxiety, and the Activity cluster was associated with improvement in Anxiety only. However, the use of clusters was not more strongly associated with improvement than individual app use. Conclusion: Participants in a field trial remained engaged with a suite of apps for the full eight weeks of the trial. App use patterns did fall into clusters, suggesting knowing something about use of one app may be useful in helping select another app that the person is more likely to use. Trial Registration: Clinicaltrials.gov NCT02176226