The concept of resilience has as its starting point the recognition that there is huge heterogeneity in people's responses to all manner of environmental adversities. Resilience is an inference based on evidence that some individuals have a better outcome than others who have experienced a comparable level of adversity; moreover, the negative experience may have either a sensitizing effect or a strengthening "steeling" effect in relation to the response to later stress or adversity. After noting the crucial importance of first testing for the environmental mediation of risk through "natural experiments," findings are reviewed on "steeling effects" in animal models and humans. Gene-environment interaction findings are considered, and it is noted that there is some evidence that the genetic influences concerns responsivity to all environments and not just bad ones. Life course effects are reviewed in relation to evidence on turning point effects associated with experiences that increase opportunities and enhance coping. Attention is drawn to both research implications and substantive findings as features that foster resilience.