During the past decade, the concept of “protective factors” has become firmly established in the field of psychiatric risk research (Garmezy, 1985; Masten & Garmezy, 1985; Rutter, 1979a, 1985a). It stems from the related notion of “resilience, ” the term used to describe the positive pole of the ubiquitous phenomenon of individual difference in people's responses to stress and adversity. For many years the phenomenon had been put aside as largely inexplicable and therefore of little interest (Ainsworth, 1962). However, the issue of individual differences would not go away, and there came a growing appreciation that it was a key topic in risk research and that an understanding of the mechanisms involved should throw crucial light on the processes involved in risk itself, as well as having implications for prevention and intervention (Rutter, 1979a). Thus, in 1972, the study of individual differences was singled out as the most important development in “maternal deprivation” research (Rutter, 1972).

Although it is difficult to identify the roots of the upsurge of interest in resilience, three fields of research clearly played crucial roles. First, the consistency of the findings of marked variations in outcomes in the quantitative research with high-risk populations, such as that into the offspring of mentally ill parents (Rutter, 1966, 1987a), forced investigators to appreciate how many children seemed to escape relatively unscathed. Second, research into temperament following the pioneering lead of Thomas, Birch, Chess, Hertzig, and Korn (1963) provided empirical evidence that children's qualities did indeed influence their responses to a variety of stress situations (Rutter, 1977). Third, Adolf Meyer (1957) had long argued for the developmental importance of the ways in which people met key life changes and transitions.