PROJECT SUMMARY Adolescence is a common period of time for suicidal ideation to emerge and thereby presents a critical opportunity for intervention. A key to reducing suicidal ideation during adolescence is to thoroughly understand how potential intervention targets may operate. The present investigation focuses on positive future thinking, a psychological process that has long been assumed to protect against risk of clinical outcomes such as suicide and thus increasingly become an intervention target. Recent work suggests that certain manifestations of positive future thinking may be counterintuitively harmful and may in fact confer greater risk of internal distress and suicidal thoughts and behaviors. Despite its potential clinical implications, there is surprisingly little work on this topic—mostly limited to measures of future thinking that may not generalize to real-world settings and limited to adult samples. Never has there been a formal study of potentially harmful effects of positive future thinking among suicidal adolescents. Aligned with our long-term goal to disrupt the trajectory toward suicide by intervening on malleable psychological mechanisms underlying suicide risk, the immediate goal of this R21 proposal is to study whether and how discrete aspects of positive future thinking may perpetuate suicidal ideation among adolescents. With a sample of 110 adolescents with past year history of suicidal ideation, the present research team will measure positive future thinking and corresponding motivational processes through baseline assessments and via ecological momentary assessment (EMA). Specific Aims are to: (1) Test whether adolescents’ experience of imagining ‘intrapersonal well-being’ (IWB)-themed desired future outcomes predicts subsequent suicidal ideation; (2) Test whether adolescents’ experience of imagining unattained desired future outcomes predicts subsequent suicidal ideation; and (3) Identify motivational processes that may account for the maladaptive effects of imagining IWB-themed and unattained desired future outcomes. This proposal is innovative because: (a) it features the most topographically rich examination of positive future thinking ever conducted among suicidal individuals; (b) it features the most ecologically valid assessment of positive future thinking ever conducted among suicidal individuals; and (c) it is conceptually radical. Exploring this highly novel yet plausible research question may not only inform the development of more focused interventions but also refine numerous extant interventions. Thoroughly vetting presumed intervention targets during a time when suicidal individuals begin engaging in psychotherapy may help prevent adverse effects of treatment and more definitively reduce suicide risk both in and out of standard treatment settings.