Research over the last two decades has established Adverse Childhood Experiences (ACEs) as one of the most important determinants of mental and physical health outcomes over the lifespan. Despite compelling evidence, the integration of Adverse Childhood Experiences (ACEs) or trauma-informed approaches into public health policies and healthcare services has been slow, underscoring the urgent need for heightened awareness and advocacy. This chapter provides an in-depth exploration of ACE studies, beginning with their origins, followed by discussions on defining ACEs and exploring various types. Subsequently, the chapter scrutinizes the evidence linking ACE exposure to prevalent mental health conditions, with a special focus on recent evidence from Asian and African countries. Finally, it synthesizes potential biological and psychological mechanisms through which ACEs get “under the skin.”