Neurobiological pathways from trauma exposure to child mental health outcomes in a high adversity South African Birth Cohort Children growing up in many low and middle income country (LMIC) contexts are at high risk of exposure to trauma, such as domestic or community violence, child abuse, or severe injury. Exposure to such adversity has been identified as a major contributor to psychological disorders in children. The negative impacts of childhood trauma exposure have been found to persist into adulthood, with wide ranging individual and societal consequences. Indeed, individuals exposed to childhood trauma are disproportionately represented among the most vulnerable groups in societies worldwide (e.g., the homeless). Despite this robust evidence of the detrimental effects of trauma exposure, there are key limitations to our understanding of this problem. First, the majority of relevant evidence derives from high income countries, rather than from LMICs, where exposure to childhood trauma is substantially more common and many children experience multiple adversities. Consequently, we have limited knowledge of the impact of childhood trauma as experienced in the types of contexts in which the majority of the world's children live. This, in turn, undermines capacity for targeted prevention or intervention in such settings. Second, there is extremely limited understanding of the underlying mechanisms that link early trauma with negative mental health outcomes, particularly considering biological processes. Our understanding of how trauma becomes embedded in the brain and body in children, and how that, in turn, confers risk of multiple psychological disorders, is particularly limited.  We plan to address limitations in our understanding of the mental health consequences of trauma in children through capitalizing on and extending a key South African birth cohort, the Drakenstein Child Health Study (DCHS). Childhood trauma is a major mental health related concern in South Africa, particularly due to high levels of interpersonal violence (including high rates of community violence, intimate partner violence and child maltreatment). We propose to conduct an in depth study of the mental health impacts of childhood trauma in this cohort, which will address limitations in our understanding and achieve a major change in knowledge in an area of key importance for LMIC contexts. The DCHS is exceptional in having repeatedly measured child trauma exposure during the first years of life, and having simultaneously completed biological assessments and measures of child mental health at multiple times points. High rates of trauma exposure among children in the DCHS mean that it provides an opportunity to study the impact of childhood trauma which is not afforded by birth cohorts based in high income country contexts, in which very few children are exposed to severe or recurrent trauma. We plan to follow-up children in the DCHS cohort at age 8-9 years, when many common psychological disorders manifest for the first time in children. Because we have measures of both exposure to trauma and biological processes which are repeated over time, we will be able to understand how trauma influences stress-related biological systems, and how those effects, in turn, may lead to psychological disorder in children. We will be able to study key biological systems involved in the body's response to stress, the immune system (which is increasingly being understood to be closely related to stress), and brain development. Through identifying pathways from trauma to psychological disorders in children, this work may change the way we provide interventions in the future. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.