This Monograph tests a theory proposing that high levels of conflict between parents leads to an increased child risk for mental health difficulties by shaking the child's sense of security in the family. Signs of child insecurity in face of interparental conflict are reflected in: a.) greater fear and distress, b.) prolonged attempts to become involved in or avoid parental conflicts, and c.) negative evaluations of the implications parental conflict has for the well-being of the family and self. Consistent with this theory, child reports of fear, avoidance, and involvement were prominent responses to interparental conflict, especially relative to reactions predicted by other theories. Moreover, interparental conflict was associated with greater insecurity in children. And this insecurity was associated with greater mental health difficulties, even when considering the role of prior mental health, child perceptions of parental conflict, and parent-child relations. The strength of these associations further depended on the quality of the larger family context.