Attraction and hostility find expression in almost every variety of human relationship, and have consequently provided a central theme for social psychology since its beginnings. Yet attempts to conceptualize the diverse phenomena embraced in these terms have produced theories of such wide generality that they have little explanatory or predictive force. The object of the present study is to bring precision to a vast and sprawling area by setting limits and dimensions to the phenomena and investigating them experimentally on the basis of a series of hypotheses derived from a critical analysis of current conceptual approaches, including frustration, need-satisfaction, and dissonance models.The programme of experimental studies focuses on cognitive validation-a motivation to form and maintain subjectively valid evaluations of the self and the social environment-which is shown to be a common denominator of a number of attraction and hostility measures. The results throw light on reactions to boastfulness and to self-debasement; impressions of persons who are described by biased informants; effects of self-evaluation on competitiveness, and the projection of unfavourable characteristics.The interest of the study for social psychologists derives both from its theoretical integration of a wide range of behaviour and from its contribution to experimental design.Albert Pepitone is professor emeritus of Psychology at the University of Pennsylvania. He is also associated with the Solomon Asch Center created in 1998 whose purpose is to identify the origins, course, and impact of violent intergroup struggles. Attraction and Hostility was his first book, although he has contributed to other volumes and has been a frequent contributor to scholarly journals. Before joining the Pennsylvania faculty in 1951, Pepitone was at the Research Center for Group Dynamics at the Massachusetts Institute of Technology and was project director at the Institute for Social Research at the University of Michigan. In 1967 he was awarded a Fulbright Scholarship to Italy.