Variability in response to stressful environmental exposures is at the core of resilience research. In order to understand why some individuals show resilient functioning in the face of adversity, one needs to understand the mechanisms through which risky environments lead to pathology in some and not others, and the ways in which risk and protective factors affect these processes. Understanding the interplay between genetic and biological processes and different environments is necessary in order to elucidate the causal pathways through which individuals show resilience or vulnerability in the face of adversity.