Millions of children across the world are affected by war and displacement. As well as having experienced traumatic war-related events, many refugee children end up living in adverse conditions with little access to basic resources. It is well established that children exposed to war and displacement are at increased risk for the development of mental health problems, including post-traumatic stress disorder, anxiety, depression, and behavioural problems. I will first introduce the Biological Pathways of Risk and Resilience in Syrian Refugee Children study (BIOPATH), which we conducted over the last 10 years in order to investigate the complex interplay between psychosocial and biological factors in the development of risk and resilience among a large sample of vulnerable Syrian refugee children (N = 1,600) living in informal refugee settlements in Lebanon. Then, I will report key findings from the BIOPATH study, including the prevalence and predictors of mental health problems, predictors of resilience, the development of resilience over time, the relationship between war exposure, hair cortisol levels and epigenetic factors (i.e., DNA methylation), as well as the role of the trait of environmental sensitivity for refugee children’s mental health.