Background: Adolescents’ beliefs about what causes depression may inform their attempts to manage the disorder and, consequently, their clinical outcomes. However, research is needed to articulate what these beliefs are and how they relate to other clinical constructs. Methods: This study explored the causal beliefs about depression held by a sample of U.S. adolescents with elevated depression symptoms (N = 281). Qualitative methods were used to identify causal beliefs from open-ended survey responses. Quantitative methods compared the perceived causes of one’s own depression vs others’ depression, compared causal beliefs across groups, and measured the association between causal beliefs and additional clinical constructs. Results: The most common causal beliefs were dysfunctional home and family relationships (52%) and stress from school (42%). Several causal beliefs were expressed more in regards to one’s own depression than others’ depression (e.g., adverse childhood events, 11% vs 3%, p = .004) and vice versa (e.g., social media use, 12% vs 2%, p < .001). Additionally, significant relationships emerged between certain causal beliefs and demographic and clinical variables. Limitations: This study did not examine behavioral indicators of illness management (e.g., help-seeking) and cannot speak to the relationship of causal beliefs to these behaviors. Moreover, as causal beliefs were measured dichotomously, we were unable to measure the degree of agreement with each belief. Conclusions: Adolescents’ causal beliefs about depression are diverse and multifaceted. The causal beliefs endorsed about one’s own depression differ substantially from those endorsed about depression generally, and both types of causal beliefs are associated with additional clinical variables.