Project Abstract Suicide is the second leading cause of death for youth aged 10-12. Recent data from the CDC show that girls have greater rates of STBs than boys—1 in 3 adolescent girls consider attempting suicide. However, we know relatively little about what factors contribute to risk for suicide in preteen girls aside from exposure to childhood adversities such as experiencing threat (e.g., interpersonal violence). Our team’s research program investigates biological responses to interpersonal stressors as a mechanism linking childhood threat exposure and suicidal thoughts and behaviors (STBs) in adolescent girls. However, to improve early identification and intervention efforts, there is a critical need to identify STB risk factors that precede this biological sensitivity to interpersonal stressors that occurs later in pubertal development. Social motivation (SM) toward peers and peripubertal hormones typically increase during preteen years prior to adolescent biological sensitization to interpersonal stressors. The purpose of the current study is to investigate SM as a novel risk factor linking childhood threat exposure with STB risk in preteen girls. Aim 1 will refine existing assessments of SM and STBs for use in a diverse set of preteen girls. Aim 2 will test our theory that maladaptive SM (e.g., high desire to avoid social failure and low effort to engage with others) contributes to preteen emergence of STBs, particularly among girls with advanced pubertal timing. Aim 3 will evaluate whether childhood threat exposure predicts both STBs and maladaptive SM in the preteen years. Aim 3 will also test our preteen STB risk pathway, which posits that childhood threat exposure increases risk for STBs via maladaptive SM. Finally, exploratory Aim 4 will examine whether this novel risk pathway is exacerbated in girls with advanced pubertal timing. We will enroll 200 preteens (ages 8-11) assigned female at birth, premenarchal at baseline, and enriched for childhood threat exposure. Assessments will occur at baseline, 6- and 12-months. All visits will have questionnaires/interviews assessing STBs, psychopathology, childhood threat exposure, and SM, along with SM behavioral assessments. Visits will include 4-week ecological momentary assessments (2x daily) and saliva acquisition (x6) for hormone assay. Two Advisory Boards will collaborate with us on measure refinement, data collection, and result dissemination: (1) adult community leaders and caregivers and (2) preteen/teen girls with lived experience relevant to this investigation. Understanding the proposed associations and mechanisms is a critical first step to identifying specific and focused targets for preventive interventions. Thus, the current research proposal will have a high impact on the field by contributing important knowledge to suicide prevention efforts in preteen girls.