As humans, we have a unique capacity to theorize about our experiences, including our emotions. We develop implicit theories about the nature of emotions, and these beliefs are consequential, guiding whether and how we try to influence our emotions and how we feel as a consequence. One fundamental belief about emotions concerns whether emotions are relatively controllable or uncontrollable. I propose that believing emotions are uncontrollable (entity beliefs) should reduce individuals’ use of emotion regulation strategies that could help them change their emotional experiences (e.g., cognitive reappraisal). This, in turn, could negatively influence psychological health (e.g., depressive symptoms). This model holds particular relevance during youth, when beliefs about emotions first develop and stabilize and when maladaptive beliefs could contribute to the rising depression rates that characterize adolescence. In the present investigation, a pilot diary study (N=223, aged 21-60) demonstrated that individuals’ entity beliefs predicted less use of cognitive reappraisal in everyday life. Then, two studies examined whether entity beliefs set youths on a maladaptive trajectory: In a cross-sectional study (N=136, aged 14-18), youths with stronger entity beliefs experienced more depressive symptoms because they used reappraisal less frequently. This pattern was replicated and extended in a longitudinal study (N=227, aged 10-18), where depressive symptoms were assessed using youth and parent reports 18 months after assessing beliefs. These results suggest that entity beliefs about emotion are risk factors for depression that act via emotion regulation. Because beliefs are still developing in youths, targeting youths’ beliefs represents an important avenue for prevention and intervention.