Nongenetic factors have a major influence on psychopathology. Knowledge on specificpsychosocial risk and protective mechanisms is more limited because of inadequate attention tomeasurement issues, person effects on the environment, and the possibility of genetic mediation.Nevertheless, a range of research strategies may be used to provide rigorous tests of causalhypotheses; these have shown the importance of environmentally mediated risks. Challenges forthe future include greater use of such research strategies, improved measures of psychosocialrisks that can be applied to large samples, investigation of origins of risks, identification ofcauses of time trends in levels of psychopathology, delineation of psychosocial effects onlifetime liability, understanding of environmental effects on the organism, appreciation ofprocesses involved in developmental programming, and understanding of individual differencesin susceptibility.